This is libc.info, produced by makeinfo version 5.1 from libc.texinfo. This is ‘The GNU C Library Reference Manual’, for version 2.36 (Arm). Copyright © 1993–2022 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being “Free Software Needs Free Documentation” and “GNU Lesser General Public License”, the Front-Cover texts being “A GNU Manual”, and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF’s Back-Cover Text is: “You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom.” INFO-DIR-SECTION Software libraries START-INFO-DIR-ENTRY * Libc: (libc). C library. END-INFO-DIR-ENTRY INFO-DIR-SECTION GNU C library functions and macros START-INFO-DIR-ENTRY * ALTWERASE: (libc)Local Modes. * ARGP_ERR_UNKNOWN: (libc)Argp Parser Functions. * ARG_MAX: (libc)General Limits. * BC_BASE_MAX: (libc)Utility Limits. * BC_DIM_MAX: (libc)Utility Limits. * BC_SCALE_MAX: (libc)Utility Limits. * BC_STRING_MAX: (libc)Utility Limits. * BRKINT: (libc)Input Modes. * BUFSIZ: (libc)Controlling Buffering. * CCTS_OFLOW: (libc)Control Modes. * CHAR_BIT: (libc)Width of Type. * CHILD_MAX: (libc)General Limits. * CIGNORE: (libc)Control Modes. * CLK_TCK: (libc)Processor Time. * CLOCAL: (libc)Control Modes. * CLOCKS_PER_SEC: (libc)CPU Time. * CLOCK_MONOTONIC: (libc)Getting the Time. * CLOCK_REALTIME: (libc)Getting the Time. * COLL_WEIGHTS_MAX: (libc)Utility Limits. * CPU_CLR: (libc)CPU Affinity. * CPU_FEATURE_ACTIVE: (libc)X86. * CPU_FEATURE_PRESENT: (libc)X86. * CPU_ISSET: (libc)CPU Affinity. * CPU_SET: (libc)CPU Affinity. * CPU_SETSIZE: (libc)CPU Affinity. * CPU_ZERO: (libc)CPU Affinity. * CREAD: (libc)Control Modes. * CRTS_IFLOW: (libc)Control Modes. * CS5: (libc)Control Modes. * CS6: (libc)Control Modes. * CS7: (libc)Control Modes. * CS8: (libc)Control Modes. * CSIZE: (libc)Control Modes. * CSTOPB: (libc)Control Modes. * DLFO_EH_SEGMENT_TYPE: (libc)Dynamic Linker Introspection. * DLFO_STRUCT_HAS_EH_COUNT: (libc)Dynamic Linker Introspection. * DLFO_STRUCT_HAS_EH_DBASE: (libc)Dynamic Linker Introspection. * DTTOIF: (libc)Directory Entries. * E2BIG: (libc)Error Codes. * EACCES: (libc)Error Codes. * EADDRINUSE: (libc)Error Codes. * EADDRNOTAVAIL: (libc)Error Codes. * EADV: (libc)Error Codes. * EAFNOSUPPORT: (libc)Error Codes. * EAGAIN: (libc)Error Codes. * EALREADY: (libc)Error Codes. * EAUTH: (libc)Error Codes. * EBACKGROUND: (libc)Error Codes. * EBADE: (libc)Error Codes. * EBADF: (libc)Error Codes. * EBADFD: (libc)Error Codes. * EBADMSG: (libc)Error Codes. * EBADR: (libc)Error Codes. * EBADRPC: (libc)Error Codes. * EBADRQC: (libc)Error Codes. * EBADSLT: (libc)Error Codes. * EBFONT: (libc)Error Codes. * EBUSY: (libc)Error Codes. * ECANCELED: (libc)Error Codes. * ECHILD: (libc)Error Codes. * ECHO: (libc)Local Modes. * ECHOCTL: (libc)Local Modes. * ECHOE: (libc)Local Modes. * ECHOK: (libc)Local Modes. * ECHOKE: (libc)Local Modes. * ECHONL: (libc)Local Modes. * ECHOPRT: (libc)Local Modes. * ECHRNG: (libc)Error Codes. * ECOMM: (libc)Error Codes. * ECONNABORTED: (libc)Error Codes. * ECONNREFUSED: (libc)Error Codes. * ECONNRESET: (libc)Error Codes. * ED: (libc)Error Codes. * EDEADLK: (libc)Error Codes. * EDEADLOCK: (libc)Error Codes. * EDESTADDRREQ: (libc)Error Codes. * EDIED: (libc)Error Codes. * EDOM: (libc)Error Codes. * EDOTDOT: (libc)Error Codes. * EDQUOT: (libc)Error Codes. * EEXIST: (libc)Error Codes. * EFAULT: (libc)Error Codes. * EFBIG: (libc)Error Codes. * EFTYPE: (libc)Error Codes. * EGRATUITOUS: (libc)Error Codes. * EGREGIOUS: (libc)Error Codes. * EHOSTDOWN: (libc)Error Codes. * EHOSTUNREACH: (libc)Error Codes. * EHWPOISON: (libc)Error Codes. * EIDRM: (libc)Error Codes. * EIEIO: (libc)Error Codes. * EILSEQ: (libc)Error Codes. * EINPROGRESS: (libc)Error Codes. * EINTR: (libc)Error Codes. * EINVAL: (libc)Error Codes. * EIO: (libc)Error Codes. * EISCONN: (libc)Error Codes. * EISDIR: (libc)Error Codes. * EISNAM: (libc)Error Codes. * EKEYEXPIRED: (libc)Error Codes. * EKEYREJECTED: (libc)Error Codes. * EKEYREVOKED: (libc)Error Codes. * EL2HLT: (libc)Error Codes. * EL2NSYNC: (libc)Error Codes. * EL3HLT: (libc)Error Codes. * EL3RST: (libc)Error Codes. * ELIBACC: (libc)Error Codes. * ELIBBAD: (libc)Error Codes. * ELIBEXEC: (libc)Error Codes. * ELIBMAX: (libc)Error Codes. * ELIBSCN: (libc)Error Codes. * ELNRNG: (libc)Error Codes. * ELOOP: (libc)Error Codes. * EMEDIUMTYPE: (libc)Error Codes. * EMFILE: (libc)Error Codes. * EMLINK: (libc)Error Codes. * EMSGSIZE: (libc)Error Codes. * EMULTIHOP: (libc)Error Codes. * ENAMETOOLONG: (libc)Error Codes. * ENAVAIL: (libc)Error Codes. * ENEEDAUTH: (libc)Error Codes. * ENETDOWN: (libc)Error Codes. * ENETRESET: (libc)Error Codes. * ENETUNREACH: (libc)Error Codes. * ENFILE: (libc)Error Codes. * ENOANO: (libc)Error Codes. * ENOBUFS: (libc)Error Codes. * ENOCSI: (libc)Error Codes. * ENODATA: (libc)Error Codes. * ENODEV: (libc)Error Codes. * ENOENT: (libc)Error Codes. * ENOEXEC: (libc)Error Codes. * ENOKEY: (libc)Error Codes. * ENOLCK: (libc)Error Codes. * ENOLINK: (libc)Error Codes. * ENOMEDIUM: (libc)Error Codes. * ENOMEM: (libc)Error Codes. * ENOMSG: (libc)Error Codes. * ENONET: (libc)Error Codes. * ENOPKG: (libc)Error Codes. * ENOPROTOOPT: (libc)Error Codes. * ENOSPC: (libc)Error Codes. * ENOSR: (libc)Error Codes. * ENOSTR: (libc)Error Codes. * ENOSYS: (libc)Error Codes. * ENOTBLK: (libc)Error Codes. * ENOTCONN: (libc)Error Codes. * ENOTDIR: (libc)Error Codes. * ENOTEMPTY: (libc)Error Codes. * ENOTNAM: (libc)Error Codes. * ENOTRECOVERABLE: (libc)Error Codes. * ENOTSOCK: (libc)Error Codes. * ENOTSUP: (libc)Error Codes. * ENOTTY: (libc)Error Codes. * ENOTUNIQ: (libc)Error Codes. * ENXIO: (libc)Error Codes. * EOF: (libc)EOF and Errors. * EOPNOTSUPP: (libc)Error Codes. * EOVERFLOW: (libc)Error Codes. * EOWNERDEAD: (libc)Error Codes. * EPERM: (libc)Error Codes. * EPFNOSUPPORT: (libc)Error Codes. * EPIPE: (libc)Error Codes. * EPROCLIM: (libc)Error Codes. * EPROCUNAVAIL: (libc)Error Codes. * EPROGMISMATCH: (libc)Error Codes. * EPROGUNAVAIL: (libc)Error Codes. * EPROTO: (libc)Error Codes. * EPROTONOSUPPORT: (libc)Error Codes. * EPROTOTYPE: (libc)Error Codes. * EQUIV_CLASS_MAX: (libc)Utility Limits. * ERANGE: (libc)Error Codes. * EREMCHG: (libc)Error Codes. * EREMOTE: (libc)Error Codes. * EREMOTEIO: (libc)Error Codes. * ERESTART: (libc)Error Codes. * ERFKILL: (libc)Error Codes. * EROFS: (libc)Error Codes. * ERPCMISMATCH: (libc)Error Codes. * ESHUTDOWN: (libc)Error Codes. * ESOCKTNOSUPPORT: (libc)Error Codes. * ESPIPE: (libc)Error Codes. * ESRCH: (libc)Error Codes. * ESRMNT: (libc)Error Codes. * ESTALE: (libc)Error Codes. * ESTRPIPE: (libc)Error Codes. * ETIME: (libc)Error Codes. * ETIMEDOUT: (libc)Error Codes. * ETOOMANYREFS: (libc)Error Codes. * ETXTBSY: (libc)Error Codes. * EUCLEAN: (libc)Error Codes. * EUNATCH: (libc)Error Codes. * EUSERS: (libc)Error Codes. * EWOULDBLOCK: (libc)Error Codes. * EXDEV: (libc)Error Codes. * EXFULL: (libc)Error Codes. * EXIT_FAILURE: (libc)Exit Status. * EXIT_SUCCESS: (libc)Exit Status. * EXPR_NEST_MAX: (libc)Utility Limits. * FD_CLOEXEC: (libc)Descriptor Flags. * FD_CLR: (libc)Waiting for I/O. * FD_ISSET: (libc)Waiting for I/O. * FD_SET: (libc)Waiting for I/O. * FD_SETSIZE: (libc)Waiting for I/O. * FD_ZERO: (libc)Waiting for I/O. * FE_SNANS_ALWAYS_SIGNAL: (libc)Infinity and NaN. * FILENAME_MAX: (libc)Limits for Files. * FLUSHO: (libc)Local Modes. * FOPEN_MAX: (libc)Opening Streams. * FP_ILOGB0: (libc)Exponents and Logarithms. * FP_ILOGBNAN: (libc)Exponents and Logarithms. * FP_LLOGB0: (libc)Exponents and Logarithms. * FP_LLOGBNAN: (libc)Exponents and Logarithms. * F_DUPFD: (libc)Duplicating Descriptors. * F_GETFD: (libc)Descriptor Flags. * F_GETFL: (libc)Getting File Status Flags. * F_GETLK: (libc)File Locks. * F_GETOWN: (libc)Interrupt Input. * F_OFD_GETLK: (libc)Open File Description Locks. * F_OFD_SETLK: (libc)Open File Description Locks. * F_OFD_SETLKW: (libc)Open File Description Locks. * F_OK: (libc)Testing File Access. * F_SETFD: (libc)Descriptor Flags. * F_SETFL: (libc)Getting File Status Flags. * F_SETLK: (libc)File Locks. * F_SETLKW: (libc)File Locks. * F_SETOWN: (libc)Interrupt Input. * HUGE_VAL: (libc)Math Error Reporting. * HUGE_VALF: (libc)Math Error Reporting. * HUGE_VALL: (libc)Math Error Reporting. * HUGE_VAL_FN: (libc)Math Error Reporting. * HUGE_VAL_FNx: (libc)Math Error Reporting. * HUPCL: (libc)Control Modes. * I: (libc)Complex Numbers. * ICANON: (libc)Local Modes. * ICRNL: (libc)Input Modes. * IEXTEN: (libc)Local Modes. * IFNAMSIZ: (libc)Interface Naming. * IFTODT: (libc)Directory Entries. * IGNBRK: (libc)Input Modes. * IGNCR: (libc)Input Modes. * IGNPAR: (libc)Input Modes. * IMAXBEL: (libc)Input Modes. * INADDR_ANY: (libc)Host Address Data Type. * INADDR_BROADCAST: (libc)Host Address Data Type. * INADDR_LOOPBACK: (libc)Host Address Data Type. * INADDR_NONE: (libc)Host Address Data Type. * INFINITY: (libc)Infinity and NaN. * INLCR: (libc)Input Modes. * INPCK: (libc)Input Modes. * IPPORT_RESERVED: (libc)Ports. * IPPORT_USERRESERVED: (libc)Ports. * ISIG: (libc)Local Modes. * ISTRIP: (libc)Input Modes. * IXANY: (libc)Input Modes. * IXOFF: (libc)Input Modes. * IXON: (libc)Input Modes. * LINE_MAX: (libc)Utility Limits. * LINK_MAX: (libc)Limits for Files. * L_ctermid: (libc)Identifying the Terminal. * L_cuserid: (libc)Who Logged In. * L_tmpnam: (libc)Temporary Files. * MAXNAMLEN: (libc)Limits for Files. * MAXSYMLINKS: (libc)Symbolic Links. * MAX_CANON: (libc)Limits for Files. * MAX_INPUT: (libc)Limits for Files. * MB_CUR_MAX: (libc)Selecting the Conversion. * MB_LEN_MAX: (libc)Selecting the Conversion. * MDMBUF: (libc)Control Modes. * MSG_DONTROUTE: (libc)Socket Data Options. * MSG_OOB: (libc)Socket Data Options. * MSG_PEEK: (libc)Socket Data Options. * NAME_MAX: (libc)Limits for Files. * NAN: (libc)Infinity and NaN. * NCCS: (libc)Mode Data Types. * NGROUPS_MAX: (libc)General Limits. * NOFLSH: (libc)Local Modes. * NOKERNINFO: (libc)Local Modes. * NSIG: (libc)Standard Signals. * NULL: (libc)Null Pointer Constant. * ONLCR: (libc)Output Modes. * ONOEOT: (libc)Output Modes. * OPEN_MAX: (libc)General Limits. * OPOST: (libc)Output Modes. * OXTABS: (libc)Output Modes. * O_ACCMODE: (libc)Access Modes. * O_APPEND: (libc)Operating Modes. * O_ASYNC: (libc)Operating Modes. * O_CREAT: (libc)Open-time Flags. * O_DIRECTORY: (libc)Open-time Flags. * O_EXCL: (libc)Open-time Flags. * O_EXEC: (libc)Access Modes. * O_EXLOCK: (libc)Open-time Flags. * O_FSYNC: (libc)Operating Modes. * O_IGNORE_CTTY: (libc)Open-time Flags. * O_NDELAY: (libc)Operating Modes. * O_NOATIME: (libc)Operating Modes. * O_NOCTTY: (libc)Open-time Flags. * O_NOFOLLOW: (libc)Open-time Flags. * O_NOLINK: (libc)Open-time Flags. * O_NONBLOCK: (libc)Open-time Flags. * O_NONBLOCK: (libc)Operating Modes. * O_NOTRANS: (libc)Open-time Flags. * O_PATH: (libc)Access Modes. * O_RDONLY: (libc)Access Modes. * O_RDWR: (libc)Access Modes. * O_READ: (libc)Access Modes. * O_SHLOCK: (libc)Open-time Flags. * O_SYNC: (libc)Operating Modes. * O_TMPFILE: (libc)Open-time Flags. * O_TRUNC: (libc)Open-time Flags. * O_WRITE: (libc)Access Modes. * O_WRONLY: (libc)Access Modes. * PARENB: (libc)Control Modes. * PARMRK: (libc)Input Modes. * PARODD: (libc)Control Modes. * PATH_MAX: (libc)Limits for Files. * PA_FLAG_MASK: (libc)Parsing a Template String. * PENDIN: (libc)Local Modes. * PF_FILE: (libc)Local Namespace Details. * PF_INET6: (libc)Internet Namespace. * PF_INET: (libc)Internet Namespace. * PF_LOCAL: (libc)Local Namespace Details. * PF_UNIX: (libc)Local Namespace Details. * PIPE_BUF: (libc)Limits for Files. * PTHREAD_ATTR_NO_SIGMASK_NP: (libc)Initial Thread Signal Mask. * P_tmpdir: (libc)Temporary Files. * RAND_MAX: (libc)ISO Random. * RE_DUP_MAX: (libc)General Limits. * RLIM_INFINITY: (libc)Limits on Resources. * RSEQ_SIG: (libc)Restartable Sequences. * R_OK: (libc)Testing File Access. * SA_NOCLDSTOP: (libc)Flags for Sigaction. * SA_ONSTACK: (libc)Flags for Sigaction. * SA_RESTART: (libc)Flags for Sigaction. * SEEK_CUR: (libc)File Positioning. * SEEK_END: (libc)File Positioning. * SEEK_SET: (libc)File Positioning. * SIGABRT: (libc)Program Error Signals. * SIGALRM: (libc)Alarm Signals. * SIGBUS: (libc)Program Error Signals. * SIGCHLD: (libc)Job Control Signals. * SIGCLD: (libc)Job Control Signals. * SIGCONT: (libc)Job Control Signals. * SIGEMT: (libc)Program Error Signals. * SIGFPE: (libc)Program Error Signals. * SIGHUP: (libc)Termination Signals. * SIGILL: (libc)Program Error Signals. * SIGINFO: (libc)Miscellaneous Signals. * SIGINT: (libc)Termination Signals. * SIGIO: (libc)Asynchronous I/O Signals. * SIGIOT: (libc)Program Error Signals. * SIGKILL: (libc)Termination Signals. * SIGLOST: (libc)Operation Error Signals. * SIGPIPE: (libc)Operation Error Signals. * SIGPOLL: (libc)Asynchronous I/O Signals. * SIGPROF: (libc)Alarm Signals. * SIGQUIT: (libc)Termination Signals. * SIGSEGV: (libc)Program Error Signals. * SIGSTOP: (libc)Job Control Signals. * SIGSYS: (libc)Program Error Signals. * SIGTERM: (libc)Termination Signals. * SIGTRAP: (libc)Program Error Signals. * SIGTSTP: (libc)Job Control Signals. * SIGTTIN: (libc)Job Control Signals. * SIGTTOU: (libc)Job Control Signals. * SIGURG: (libc)Asynchronous I/O Signals. * SIGUSR1: (libc)Miscellaneous Signals. * SIGUSR2: (libc)Miscellaneous Signals. * SIGVTALRM: (libc)Alarm Signals. * SIGWINCH: (libc)Miscellaneous Signals. * SIGXCPU: (libc)Operation Error Signals. * SIGXFSZ: (libc)Operation Error Signals. * SIG_ERR: (libc)Basic Signal Handling. * SNAN: (libc)Infinity and NaN. * SNANF: (libc)Infinity and NaN. * SNANFN: (libc)Infinity and NaN. * SNANFNx: (libc)Infinity and NaN. * SNANL: (libc)Infinity and NaN. * SOCK_DGRAM: (libc)Communication Styles. * SOCK_RAW: (libc)Communication Styles. * SOCK_RDM: (libc)Communication Styles. * SOCK_SEQPACKET: (libc)Communication Styles. * SOCK_STREAM: (libc)Communication Styles. * SOL_SOCKET: (libc)Socket-Level Options. * SSIZE_MAX: (libc)General Limits. * STREAM_MAX: (libc)General Limits. * SUN_LEN: (libc)Local Namespace Details. * S_IFMT: (libc)Testing File Type. * S_ISBLK: (libc)Testing File Type. * S_ISCHR: (libc)Testing File Type. * S_ISDIR: (libc)Testing File Type. * S_ISFIFO: (libc)Testing File Type. * S_ISLNK: (libc)Testing File Type. * S_ISREG: (libc)Testing File Type. * S_ISSOCK: (libc)Testing File Type. * S_TYPEISMQ: (libc)Testing File Type. * S_TYPEISSEM: (libc)Testing File Type. * S_TYPEISSHM: (libc)Testing File Type. * TMP_MAX: (libc)Temporary Files. * TOSTOP: (libc)Local Modes. * TZNAME_MAX: (libc)General Limits. * VDISCARD: (libc)Other Special. * VDSUSP: (libc)Signal Characters. * VEOF: (libc)Editing Characters. * VEOL2: (libc)Editing Characters. * VEOL: (libc)Editing Characters. * VERASE: (libc)Editing Characters. * VINTR: (libc)Signal Characters. * VKILL: (libc)Editing Characters. * VLNEXT: (libc)Other Special. * VMIN: (libc)Noncanonical Input. * VQUIT: (libc)Signal Characters. * VREPRINT: (libc)Editing Characters. * VSTART: (libc)Start/Stop Characters. * VSTATUS: (libc)Other Special. * VSTOP: (libc)Start/Stop Characters. * VSUSP: (libc)Signal Characters. * VTIME: (libc)Noncanonical Input. * VWERASE: (libc)Editing Characters. * WCHAR_MAX: (libc)Extended Char Intro. * WCHAR_MIN: (libc)Extended Char Intro. * WCOREDUMP: (libc)Process Completion Status. * WEOF: (libc)EOF and Errors. * WEOF: (libc)Extended Char Intro. * WEXITSTATUS: (libc)Process Completion Status. * WIFEXITED: (libc)Process Completion Status. * WIFSIGNALED: (libc)Process Completion Status. * WIFSTOPPED: (libc)Process Completion Status. * WSTOPSIG: (libc)Process Completion Status. * WTERMSIG: (libc)Process Completion Status. * W_OK: (libc)Testing File Access. * X_OK: (libc)Testing File Access. * _Complex_I: (libc)Complex Numbers. * _Exit: (libc)Termination Internals. * _Fork: (libc)Creating a Process. * _IOFBF: (libc)Controlling Buffering. * _IOLBF: (libc)Controlling Buffering. * _IONBF: (libc)Controlling Buffering. * _Imaginary_I: (libc)Complex Numbers. * _PATH_UTMP: (libc)Manipulating the Database. * _PATH_WTMP: (libc)Manipulating the Database. * _POSIX2_C_DEV: (libc)System Options. * _POSIX2_C_VERSION: (libc)Version Supported. * _POSIX2_FORT_DEV: (libc)System Options. * _POSIX2_FORT_RUN: (libc)System Options. * _POSIX2_LOCALEDEF: (libc)System Options. * _POSIX2_SW_DEV: (libc)System Options. * _POSIX_CHOWN_RESTRICTED: (libc)Options for Files. * _POSIX_JOB_CONTROL: (libc)System Options. * _POSIX_NO_TRUNC: (libc)Options for Files. * _POSIX_SAVED_IDS: (libc)System Options. * _POSIX_VDISABLE: (libc)Options for Files. * _POSIX_VERSION: (libc)Version Supported. * __fbufsize: (libc)Controlling Buffering. * __flbf: (libc)Controlling Buffering. * __fpending: (libc)Controlling Buffering. * __fpurge: (libc)Flushing Buffers. * __freadable: (libc)Opening Streams. * __freading: (libc)Opening Streams. * __fsetlocking: (libc)Streams and Threads. * __fwritable: (libc)Opening Streams. * __fwriting: (libc)Opening Streams. * __gconv_end_fct: (libc)glibc iconv Implementation. * __gconv_fct: (libc)glibc iconv Implementation. * __gconv_init_fct: (libc)glibc iconv Implementation. * __ppc_get_timebase: (libc)PowerPC. * __ppc_get_timebase_freq: (libc)PowerPC. * __ppc_mdoio: (libc)PowerPC. * __ppc_mdoom: (libc)PowerPC. * __ppc_set_ppr_low: (libc)PowerPC. * __ppc_set_ppr_med: (libc)PowerPC. * __ppc_set_ppr_med_high: (libc)PowerPC. * __ppc_set_ppr_med_low: (libc)PowerPC. * __ppc_set_ppr_very_low: (libc)PowerPC. * __ppc_yield: (libc)PowerPC. * __riscv_flush_icache: (libc)RISC-V. * __va_copy: (libc)Argument Macros. * __x86_get_cpuid_feature_leaf: (libc)X86. * _dl_find_object: (libc)Dynamic Linker Introspection. * _exit: (libc)Termination Internals. * _flushlbf: (libc)Flushing Buffers. * _tolower: (libc)Case Conversion. * _toupper: (libc)Case Conversion. * a64l: (libc)Encode Binary Data. * abort: (libc)Aborting a Program. * abs: (libc)Absolute Value. * accept: (libc)Accepting Connections. * access: (libc)Testing File Access. * acos: (libc)Inverse Trig Functions. * acosf: (libc)Inverse Trig Functions. * acosfN: (libc)Inverse Trig Functions. * acosfNx: (libc)Inverse Trig Functions. * acosh: (libc)Hyperbolic Functions. * acoshf: (libc)Hyperbolic Functions. * acoshfN: (libc)Hyperbolic Functions. * acoshfNx: (libc)Hyperbolic Functions. * acoshl: (libc)Hyperbolic Functions. * acosl: (libc)Inverse Trig Functions. * addmntent: (libc)mtab. * addseverity: (libc)Adding Severity Classes. * adjtime: (libc)Setting and Adjusting the Time. * adjtimex: (libc)Setting and Adjusting the Time. * aio_cancel64: (libc)Cancel AIO Operations. * aio_cancel: (libc)Cancel AIO Operations. * aio_error64: (libc)Status of AIO Operations. * aio_error: (libc)Status of AIO Operations. * aio_fsync64: (libc)Synchronizing AIO Operations. * aio_fsync: (libc)Synchronizing AIO Operations. * aio_init: (libc)Configuration of AIO. * aio_read64: (libc)Asynchronous Reads/Writes. * aio_read: (libc)Asynchronous Reads/Writes. * aio_return64: (libc)Status of AIO Operations. * aio_return: (libc)Status of AIO Operations. * aio_suspend64: (libc)Synchronizing AIO Operations. * aio_suspend: (libc)Synchronizing AIO Operations. * aio_write64: (libc)Asynchronous Reads/Writes. * aio_write: (libc)Asynchronous Reads/Writes. * alarm: (libc)Setting an Alarm. * aligned_alloc: (libc)Aligned Memory Blocks. * alloca: (libc)Variable Size Automatic. * alphasort64: (libc)Scanning Directory Content. * alphasort: (libc)Scanning Directory Content. * arc4random: (libc)High Quality Random. * arc4random_buf: (libc)High Quality Random. * arc4random_uniform: (libc)High Quality Random. * argp_error: (libc)Argp Helper Functions. * argp_failure: (libc)Argp Helper Functions. * argp_help: (libc)Argp Help. * argp_parse: (libc)Argp. * argp_state_help: (libc)Argp Helper Functions. * argp_usage: (libc)Argp Helper Functions. * argz_add: (libc)Argz Functions. * argz_add_sep: (libc)Argz Functions. * argz_append: (libc)Argz Functions. * argz_count: (libc)Argz Functions. * argz_create: (libc)Argz Functions. * argz_create_sep: (libc)Argz Functions. * argz_delete: (libc)Argz Functions. * argz_extract: (libc)Argz Functions. * argz_insert: (libc)Argz Functions. * argz_next: (libc)Argz Functions. * argz_replace: (libc)Argz Functions. * argz_stringify: (libc)Argz Functions. * asctime: (libc)Formatting Calendar Time. * asctime_r: (libc)Formatting Calendar Time. * asin: (libc)Inverse Trig Functions. * asinf: (libc)Inverse Trig Functions. * asinfN: (libc)Inverse Trig Functions. * asinfNx: (libc)Inverse Trig Functions. * asinh: (libc)Hyperbolic Functions. * asinhf: (libc)Hyperbolic Functions. * asinhfN: (libc)Hyperbolic Functions. * asinhfNx: (libc)Hyperbolic Functions. * asinhl: (libc)Hyperbolic Functions. * asinl: (libc)Inverse Trig Functions. * asprintf: (libc)Dynamic Output. * assert: (libc)Consistency Checking. * assert_perror: (libc)Consistency Checking. * atan2: (libc)Inverse Trig Functions. * atan2f: (libc)Inverse Trig Functions. * atan2fN: (libc)Inverse Trig Functions. * atan2fNx: (libc)Inverse Trig Functions. * atan2l: (libc)Inverse Trig Functions. * atan: (libc)Inverse Trig Functions. * atanf: (libc)Inverse Trig Functions. * atanfN: (libc)Inverse Trig Functions. * atanfNx: (libc)Inverse Trig Functions. * atanh: (libc)Hyperbolic Functions. * atanhf: (libc)Hyperbolic Functions. * atanhfN: (libc)Hyperbolic Functions. * atanhfNx: (libc)Hyperbolic Functions. * atanhl: (libc)Hyperbolic Functions. * atanl: (libc)Inverse Trig Functions. * atexit: (libc)Cleanups on Exit. * atof: (libc)Parsing of Floats. * atoi: (libc)Parsing of Integers. * atol: (libc)Parsing of Integers. * atoll: (libc)Parsing of Integers. * backtrace: (libc)Backtraces. * backtrace_symbols: (libc)Backtraces. * backtrace_symbols_fd: (libc)Backtraces. * basename: (libc)Finding Tokens in a String. * basename: (libc)Finding Tokens in a String. * bcmp: (libc)String/Array Comparison. * bcopy: (libc)Copying Strings and Arrays. * bind: (libc)Setting Address. * bind_textdomain_codeset: (libc)Charset conversion in gettext. * bindtextdomain: (libc)Locating gettext catalog. * brk: (libc)Resizing the Data Segment. * bsearch: (libc)Array Search Function. * btowc: (libc)Converting a Character. * bzero: (libc)Copying Strings and Arrays. * cabs: (libc)Absolute Value. * cabsf: (libc)Absolute Value. * cabsfN: (libc)Absolute Value. * cabsfNx: (libc)Absolute Value. * cabsl: (libc)Absolute Value. * cacos: (libc)Inverse Trig Functions. * cacosf: (libc)Inverse Trig Functions. * cacosfN: (libc)Inverse Trig Functions. * cacosfNx: (libc)Inverse Trig Functions. * cacosh: (libc)Hyperbolic Functions. * cacoshf: (libc)Hyperbolic Functions. * cacoshfN: (libc)Hyperbolic Functions. * cacoshfNx: (libc)Hyperbolic Functions. * cacoshl: (libc)Hyperbolic Functions. * cacosl: (libc)Inverse Trig Functions. * call_once: (libc)Call Once. * calloc: (libc)Allocating Cleared Space. * canonicalize: (libc)FP Bit Twiddling. * canonicalize_file_name: (libc)Symbolic Links. * canonicalizef: (libc)FP Bit Twiddling. * canonicalizefN: (libc)FP Bit Twiddling. * canonicalizefNx: (libc)FP Bit Twiddling. * canonicalizel: (libc)FP Bit Twiddling. * carg: (libc)Operations on Complex. * cargf: (libc)Operations on Complex. * cargfN: (libc)Operations on Complex. * cargfNx: (libc)Operations on Complex. * cargl: (libc)Operations on Complex. * casin: (libc)Inverse Trig Functions. * casinf: (libc)Inverse Trig Functions. * casinfN: (libc)Inverse Trig Functions. * casinfNx: (libc)Inverse Trig Functions. * casinh: (libc)Hyperbolic Functions. * casinhf: (libc)Hyperbolic Functions. * casinhfN: (libc)Hyperbolic Functions. * casinhfNx: (libc)Hyperbolic Functions. * casinhl: (libc)Hyperbolic Functions. * casinl: (libc)Inverse Trig Functions. * catan: (libc)Inverse Trig Functions. * catanf: (libc)Inverse Trig Functions. * catanfN: (libc)Inverse Trig Functions. * catanfNx: (libc)Inverse Trig Functions. * catanh: (libc)Hyperbolic Functions. * catanhf: (libc)Hyperbolic Functions. * catanhfN: (libc)Hyperbolic Functions. * catanhfNx: (libc)Hyperbolic Functions. * catanhl: (libc)Hyperbolic Functions. * catanl: (libc)Inverse Trig Functions. * catclose: (libc)The catgets Functions. * catgets: (libc)The catgets Functions. * catopen: (libc)The catgets Functions. * cbrt: (libc)Exponents and Logarithms. * cbrtf: (libc)Exponents and Logarithms. * cbrtfN: (libc)Exponents and Logarithms. * cbrtfNx: (libc)Exponents and Logarithms. * cbrtl: (libc)Exponents and Logarithms. * ccos: (libc)Trig Functions. * ccosf: (libc)Trig Functions. * ccosfN: (libc)Trig Functions. * ccosfNx: (libc)Trig Functions. * ccosh: (libc)Hyperbolic Functions. * ccoshf: (libc)Hyperbolic Functions. * ccoshfN: (libc)Hyperbolic Functions. * ccoshfNx: (libc)Hyperbolic Functions. * ccoshl: (libc)Hyperbolic Functions. * ccosl: (libc)Trig Functions. * ceil: (libc)Rounding Functions. * ceilf: (libc)Rounding Functions. * ceilfN: (libc)Rounding Functions. * ceilfNx: (libc)Rounding Functions. * ceill: (libc)Rounding Functions. * cexp: (libc)Exponents and Logarithms. * cexpf: (libc)Exponents and Logarithms. * cexpfN: (libc)Exponents and Logarithms. * cexpfNx: (libc)Exponents and Logarithms. * cexpl: (libc)Exponents and Logarithms. * cfgetispeed: (libc)Line Speed. * cfgetospeed: (libc)Line Speed. * cfmakeraw: (libc)Noncanonical Input. * cfsetispeed: (libc)Line Speed. * cfsetospeed: (libc)Line Speed. * cfsetspeed: (libc)Line Speed. * chdir: (libc)Working Directory. * chmod: (libc)Setting Permissions. * chown: (libc)File Owner. * cimag: (libc)Operations on Complex. * cimagf: (libc)Operations on Complex. * cimagfN: (libc)Operations on Complex. * cimagfNx: (libc)Operations on Complex. * cimagl: (libc)Operations on Complex. * clearenv: (libc)Environment Access. * clearerr: (libc)Error Recovery. * clearerr_unlocked: (libc)Error Recovery. * clock: (libc)CPU Time. * clock_getres: (libc)Getting the Time. * clock_gettime: (libc)Getting the Time. * clock_settime: (libc)Setting and Adjusting the Time. * clog10: (libc)Exponents and Logarithms. * clog10f: (libc)Exponents and Logarithms. * clog10fN: (libc)Exponents and Logarithms. * clog10fNx: (libc)Exponents and Logarithms. * clog10l: (libc)Exponents and Logarithms. * clog: (libc)Exponents and Logarithms. * clogf: (libc)Exponents and Logarithms. * clogfN: (libc)Exponents and Logarithms. * clogfNx: (libc)Exponents and Logarithms. * clogl: (libc)Exponents and Logarithms. * close: (libc)Opening and Closing Files. * close_range: (libc)Opening and Closing Files. * closedir: (libc)Reading/Closing Directory. * closefrom: (libc)Opening and Closing Files. * closelog: (libc)closelog. * cnd_broadcast: (libc)ISO C Condition Variables. * cnd_destroy: (libc)ISO C Condition Variables. * cnd_init: (libc)ISO C Condition Variables. * cnd_signal: (libc)ISO C Condition Variables. * cnd_timedwait: (libc)ISO C Condition Variables. * cnd_wait: (libc)ISO C Condition Variables. * confstr: (libc)String Parameters. * conj: (libc)Operations on Complex. * conjf: (libc)Operations on Complex. * conjfN: (libc)Operations on Complex. * conjfNx: (libc)Operations on Complex. * conjl: (libc)Operations on Complex. * connect: (libc)Connecting. * copy_file_range: (libc)Copying File Data. * copysign: (libc)FP Bit Twiddling. * copysignf: (libc)FP Bit Twiddling. * copysignfN: (libc)FP Bit Twiddling. * copysignfNx: (libc)FP Bit Twiddling. * copysignl: (libc)FP Bit Twiddling. * cos: (libc)Trig Functions. * cosf: (libc)Trig Functions. * cosfN: (libc)Trig Functions. * cosfNx: (libc)Trig Functions. * cosh: (libc)Hyperbolic Functions. * coshf: (libc)Hyperbolic Functions. * coshfN: (libc)Hyperbolic Functions. * coshfNx: (libc)Hyperbolic Functions. * coshl: (libc)Hyperbolic Functions. * cosl: (libc)Trig Functions. * cpow: (libc)Exponents and Logarithms. * cpowf: (libc)Exponents and Logarithms. * cpowfN: (libc)Exponents and Logarithms. * cpowfNx: (libc)Exponents and Logarithms. * cpowl: (libc)Exponents and Logarithms. * cproj: (libc)Operations on Complex. * cprojf: (libc)Operations on Complex. * cprojfN: (libc)Operations on Complex. * cprojfNx: (libc)Operations on Complex. * cprojl: (libc)Operations on Complex. * creal: (libc)Operations on Complex. * crealf: (libc)Operations on Complex. * crealfN: (libc)Operations on Complex. * crealfNx: (libc)Operations on Complex. * creall: (libc)Operations on Complex. * creat64: (libc)Opening and Closing Files. * creat: (libc)Opening and Closing Files. * crypt: (libc)Passphrase Storage. * crypt_r: (libc)Passphrase Storage. * csin: (libc)Trig Functions. * csinf: (libc)Trig Functions. * csinfN: (libc)Trig Functions. * csinfNx: (libc)Trig Functions. * csinh: (libc)Hyperbolic Functions. * csinhf: (libc)Hyperbolic Functions. * csinhfN: (libc)Hyperbolic Functions. * csinhfNx: (libc)Hyperbolic Functions. * csinhl: (libc)Hyperbolic Functions. * csinl: (libc)Trig Functions. * csqrt: (libc)Exponents and Logarithms. * csqrtf: (libc)Exponents and Logarithms. * csqrtfN: (libc)Exponents and Logarithms. * csqrtfNx: (libc)Exponents and Logarithms. * csqrtl: (libc)Exponents and Logarithms. * ctan: (libc)Trig Functions. * ctanf: (libc)Trig Functions. * ctanfN: (libc)Trig Functions. * ctanfNx: (libc)Trig Functions. * ctanh: (libc)Hyperbolic Functions. * ctanhf: (libc)Hyperbolic Functions. * ctanhfN: (libc)Hyperbolic Functions. * ctanhfNx: (libc)Hyperbolic Functions. * ctanhl: (libc)Hyperbolic Functions. * ctanl: (libc)Trig Functions. * ctermid: (libc)Identifying the Terminal. * ctime: (libc)Formatting Calendar Time. * ctime_r: (libc)Formatting Calendar Time. * cuserid: (libc)Who Logged In. * daddl: (libc)Misc FP Arithmetic. * dcgettext: (libc)Translation with gettext. * dcngettext: (libc)Advanced gettext functions. * ddivl: (libc)Misc FP Arithmetic. * dfmal: (libc)Misc FP Arithmetic. * dgettext: (libc)Translation with gettext. * difftime: (libc)Calculating Elapsed Time. * dirfd: (libc)Opening a Directory. * dirname: (libc)Finding Tokens in a String. * div: (libc)Integer Division. * dlinfo: (libc)Dynamic Linker Introspection. * dmull: (libc)Misc FP Arithmetic. * dngettext: (libc)Advanced gettext functions. * drand48: (libc)SVID Random. * drand48_r: (libc)SVID Random. * drem: (libc)Remainder Functions. * dremf: (libc)Remainder Functions. * dreml: (libc)Remainder Functions. * dsqrtl: (libc)Misc FP Arithmetic. * dsubl: (libc)Misc FP Arithmetic. * dup2: (libc)Duplicating Descriptors. * dup: (libc)Duplicating Descriptors. * ecvt: (libc)System V Number Conversion. * ecvt_r: (libc)System V Number Conversion. * endfsent: (libc)fstab. * endgrent: (libc)Scanning All Groups. * endhostent: (libc)Host Names. * endmntent: (libc)mtab. * endnetent: (libc)Networks Database. * endnetgrent: (libc)Lookup Netgroup. * endprotoent: (libc)Protocols Database. * endpwent: (libc)Scanning All Users. * endservent: (libc)Services Database. * endutent: (libc)Manipulating the Database. * endutxent: (libc)XPG Functions. * envz_add: (libc)Envz Functions. * envz_entry: (libc)Envz Functions. * envz_get: (libc)Envz Functions. * envz_merge: (libc)Envz Functions. * envz_remove: (libc)Envz Functions. * envz_strip: (libc)Envz Functions. * erand48: (libc)SVID Random. * erand48_r: (libc)SVID Random. * erf: (libc)Special Functions. * erfc: (libc)Special Functions. * erfcf: (libc)Special Functions. * erfcfN: (libc)Special Functions. * erfcfNx: (libc)Special Functions. * erfcl: (libc)Special Functions. * erff: (libc)Special Functions. * erffN: (libc)Special Functions. * erffNx: (libc)Special Functions. * erfl: (libc)Special Functions. * err: (libc)Error Messages. * errno: (libc)Checking for Errors. * error: (libc)Error Messages. * error_at_line: (libc)Error Messages. * errx: (libc)Error Messages. * execl: (libc)Executing a File. * execle: (libc)Executing a File. * execlp: (libc)Executing a File. * execv: (libc)Executing a File. * execve: (libc)Executing a File. * execvp: (libc)Executing a File. * exit: (libc)Normal Termination. * exp10: (libc)Exponents and Logarithms. * exp10f: (libc)Exponents and Logarithms. * exp10fN: (libc)Exponents and Logarithms. * exp10fNx: (libc)Exponents and Logarithms. * exp10l: (libc)Exponents and Logarithms. * exp2: (libc)Exponents and Logarithms. * exp2f: (libc)Exponents and Logarithms. * exp2fN: (libc)Exponents and Logarithms. * exp2fNx: (libc)Exponents and Logarithms. * exp2l: (libc)Exponents and Logarithms. * exp: (libc)Exponents and Logarithms. * expf: (libc)Exponents and Logarithms. * expfN: (libc)Exponents and Logarithms. * expfNx: (libc)Exponents and Logarithms. * expl: (libc)Exponents and Logarithms. * explicit_bzero: (libc)Erasing Sensitive Data. * expm1: (libc)Exponents and Logarithms. * expm1f: (libc)Exponents and Logarithms. * expm1fN: (libc)Exponents and Logarithms. * expm1fNx: (libc)Exponents and Logarithms. * expm1l: (libc)Exponents and Logarithms. * fMaddfN: (libc)Misc FP Arithmetic. * fMaddfNx: (libc)Misc FP Arithmetic. * fMdivfN: (libc)Misc FP Arithmetic. * fMdivfNx: (libc)Misc FP Arithmetic. * fMfmafN: (libc)Misc FP Arithmetic. * fMfmafNx: (libc)Misc FP Arithmetic. * fMmulfN: (libc)Misc FP Arithmetic. * fMmulfNx: (libc)Misc FP Arithmetic. * fMsqrtfN: (libc)Misc FP Arithmetic. * fMsqrtfNx: (libc)Misc FP Arithmetic. * fMsubfN: (libc)Misc FP Arithmetic. * fMsubfNx: (libc)Misc FP Arithmetic. * fMxaddfN: (libc)Misc FP Arithmetic. * fMxaddfNx: (libc)Misc FP Arithmetic. * fMxdivfN: (libc)Misc FP Arithmetic. * fMxdivfNx: (libc)Misc FP Arithmetic. * fMxfmafN: (libc)Misc FP Arithmetic. * fMxfmafNx: (libc)Misc FP Arithmetic. * fMxmulfN: (libc)Misc FP Arithmetic. * fMxmulfNx: (libc)Misc FP Arithmetic. * fMxsqrtfN: (libc)Misc FP Arithmetic. * fMxsqrtfNx: (libc)Misc FP Arithmetic. * fMxsubfN: (libc)Misc FP Arithmetic. * fMxsubfNx: (libc)Misc FP Arithmetic. * fabs: (libc)Absolute Value. * fabsf: (libc)Absolute Value. * fabsfN: (libc)Absolute Value. * fabsfNx: (libc)Absolute Value. * fabsl: (libc)Absolute Value. * fadd: (libc)Misc FP Arithmetic. * faddl: (libc)Misc FP Arithmetic. * fchdir: (libc)Working Directory. * fchmod: (libc)Setting Permissions. * fchown: (libc)File Owner. * fclose: (libc)Closing Streams. * fcloseall: (libc)Closing Streams. * fcntl: (libc)Control Operations. * fcvt: (libc)System V Number Conversion. * fcvt_r: (libc)System V Number Conversion. * fdatasync: (libc)Synchronizing I/O. * fdim: (libc)Misc FP Arithmetic. * fdimf: (libc)Misc FP Arithmetic. * fdimfN: (libc)Misc FP Arithmetic. * fdimfNx: (libc)Misc FP Arithmetic. * fdiml: (libc)Misc FP Arithmetic. * fdiv: (libc)Misc FP Arithmetic. * fdivl: (libc)Misc FP Arithmetic. * fdopen: (libc)Descriptors and Streams. * fdopendir: (libc)Opening a Directory. * feclearexcept: (libc)Status bit operations. * fedisableexcept: (libc)Control Functions. * feenableexcept: (libc)Control Functions. * fegetenv: (libc)Control Functions. * fegetexcept: (libc)Control Functions. * fegetexceptflag: (libc)Status bit operations. * fegetmode: (libc)Control Functions. * fegetround: (libc)Rounding. * feholdexcept: (libc)Control Functions. * feof: (libc)EOF and Errors. * feof_unlocked: (libc)EOF and Errors. * feraiseexcept: (libc)Status bit operations. * ferror: (libc)EOF and Errors. * ferror_unlocked: (libc)EOF and Errors. * fesetenv: (libc)Control Functions. * fesetexcept: (libc)Status bit operations. * fesetexceptflag: (libc)Status bit operations. * fesetmode: (libc)Control Functions. * fesetround: (libc)Rounding. * fetestexcept: (libc)Status bit operations. * fetestexceptflag: (libc)Status bit operations. * feupdateenv: (libc)Control Functions. * fexecve: (libc)Executing a File. * fflush: (libc)Flushing Buffers. * fflush_unlocked: (libc)Flushing Buffers. * ffma: (libc)Misc FP Arithmetic. * ffmal: (libc)Misc FP Arithmetic. * fgetc: (libc)Character Input. * fgetc_unlocked: (libc)Character Input. * fgetgrent: (libc)Scanning All Groups. * fgetgrent_r: (libc)Scanning All Groups. * fgetpos64: (libc)Portable Positioning. * fgetpos: (libc)Portable Positioning. * fgetpwent: (libc)Scanning All Users. * fgetpwent_r: (libc)Scanning All Users. * fgets: (libc)Line Input. * fgets_unlocked: (libc)Line Input. * fgetwc: (libc)Character Input. * fgetwc_unlocked: (libc)Character Input. * fgetws: (libc)Line Input. * fgetws_unlocked: (libc)Line Input. * fileno: (libc)Descriptors and Streams. * fileno_unlocked: (libc)Descriptors and Streams. * finite: (libc)Floating Point Classes. * finitef: (libc)Floating Point Classes. * finitel: (libc)Floating Point Classes. * flockfile: (libc)Streams and Threads. * floor: (libc)Rounding Functions. * floorf: (libc)Rounding Functions. * floorfN: (libc)Rounding Functions. * floorfNx: (libc)Rounding Functions. * floorl: (libc)Rounding Functions. * fma: (libc)Misc FP Arithmetic. * fmaf: (libc)Misc FP Arithmetic. * fmafN: (libc)Misc FP Arithmetic. * fmafNx: (libc)Misc FP Arithmetic. * fmal: (libc)Misc FP Arithmetic. * fmax: (libc)Misc FP Arithmetic. * fmaxf: (libc)Misc FP Arithmetic. * fmaxfN: (libc)Misc FP Arithmetic. * fmaxfNx: (libc)Misc FP Arithmetic. * fmaximum: (libc)Misc FP Arithmetic. * fmaximum_mag: (libc)Misc FP Arithmetic. * fmaximum_mag_num: (libc)Misc FP Arithmetic. * fmaximum_mag_numf: (libc)Misc FP Arithmetic. * fmaximum_mag_numfN: (libc)Misc FP Arithmetic. * fmaximum_mag_numfNx: (libc)Misc FP Arithmetic. * fmaximum_mag_numl: (libc)Misc FP Arithmetic. * fmaximum_magf: (libc)Misc FP Arithmetic. * fmaximum_magfN: (libc)Misc FP Arithmetic. * fmaximum_magfNx: (libc)Misc FP Arithmetic. * fmaximum_magl: (libc)Misc FP Arithmetic. * fmaximum_num: (libc)Misc FP Arithmetic. * fmaximum_numf: (libc)Misc FP Arithmetic. * fmaximum_numfN: (libc)Misc FP Arithmetic. * fmaximum_numfNx: (libc)Misc FP Arithmetic. * fmaximum_numl: (libc)Misc FP Arithmetic. * fmaximumf: (libc)Misc FP Arithmetic. * fmaximumfN: (libc)Misc FP Arithmetic. * fmaximumfNx: (libc)Misc FP Arithmetic. * fmaximuml: (libc)Misc FP Arithmetic. * fmaxl: (libc)Misc FP Arithmetic. * fmaxmag: (libc)Misc FP Arithmetic. * fmaxmagf: (libc)Misc FP Arithmetic. * fmaxmagfN: (libc)Misc FP Arithmetic. * fmaxmagfNx: (libc)Misc FP Arithmetic. * fmaxmagl: (libc)Misc FP Arithmetic. * fmemopen: (libc)String Streams. * fmin: (libc)Misc FP Arithmetic. * fminf: (libc)Misc FP Arithmetic. * fminfN: (libc)Misc FP Arithmetic. * fminfNx: (libc)Misc FP Arithmetic. * fminimum: (libc)Misc FP Arithmetic. * fminimum_mag: (libc)Misc FP Arithmetic. * fminimum_mag_num: (libc)Misc FP Arithmetic. * fminimum_mag_numf: (libc)Misc FP Arithmetic. * fminimum_mag_numfN: (libc)Misc FP Arithmetic. * fminimum_mag_numfNx: (libc)Misc FP Arithmetic. * fminimum_mag_numl: (libc)Misc FP Arithmetic. * fminimum_magf: (libc)Misc FP Arithmetic. * fminimum_magfN: (libc)Misc FP Arithmetic. * fminimum_magfNx: (libc)Misc FP Arithmetic. * fminimum_magl: (libc)Misc FP Arithmetic. * fminimum_num: (libc)Misc FP Arithmetic. * fminimum_numf: (libc)Misc FP Arithmetic. * fminimum_numfN: (libc)Misc FP Arithmetic. * fminimum_numfNx: (libc)Misc FP Arithmetic. * fminimum_numl: (libc)Misc FP Arithmetic. * fminimumf: (libc)Misc FP Arithmetic. * fminimumfN: (libc)Misc FP Arithmetic. * fminimumfNx: (libc)Misc FP Arithmetic. * fminimuml: (libc)Misc FP Arithmetic. * fminl: (libc)Misc FP Arithmetic. * fminmag: (libc)Misc FP Arithmetic. * fminmagf: (libc)Misc FP Arithmetic. * fminmagfN: (libc)Misc FP Arithmetic. * fminmagfNx: (libc)Misc FP Arithmetic. * fminmagl: (libc)Misc FP Arithmetic. * fmod: (libc)Remainder Functions. * fmodf: (libc)Remainder Functions. * fmodfN: (libc)Remainder Functions. * fmodfNx: (libc)Remainder Functions. * fmodl: (libc)Remainder Functions. * fmtmsg: (libc)Printing Formatted Messages. * fmul: (libc)Misc FP Arithmetic. * fmull: (libc)Misc FP Arithmetic. * fnmatch: (libc)Wildcard Matching. * fopen64: (libc)Opening Streams. * fopen: (libc)Opening Streams. * fopencookie: (libc)Streams and Cookies. * fork: (libc)Creating a Process. * forkpty: (libc)Pseudo-Terminal Pairs. * fpathconf: (libc)Pathconf. * fpclassify: (libc)Floating Point Classes. * fprintf: (libc)Formatted Output Functions. * fputc: (libc)Simple Output. * fputc_unlocked: (libc)Simple Output. * fputs: (libc)Simple Output. * fputs_unlocked: (libc)Simple Output. * fputwc: (libc)Simple Output. * fputwc_unlocked: (libc)Simple Output. * fputws: (libc)Simple Output. * fputws_unlocked: (libc)Simple Output. * fread: (libc)Block Input/Output. * fread_unlocked: (libc)Block Input/Output. * free: (libc)Freeing after Malloc. * freopen64: (libc)Opening Streams. * freopen: (libc)Opening Streams. * frexp: (libc)Normalization Functions. * frexpf: (libc)Normalization Functions. * frexpfN: (libc)Normalization Functions. * frexpfNx: (libc)Normalization Functions. * frexpl: (libc)Normalization Functions. * fromfp: (libc)Rounding Functions. * fromfpf: (libc)Rounding Functions. * fromfpfN: (libc)Rounding Functions. * fromfpfNx: (libc)Rounding Functions. * fromfpl: (libc)Rounding Functions. * fromfpx: (libc)Rounding Functions. * fromfpxf: (libc)Rounding Functions. * fromfpxfN: (libc)Rounding Functions. * fromfpxfNx: (libc)Rounding Functions. * fromfpxl: (libc)Rounding Functions. * fscanf: (libc)Formatted Input Functions. * fseek: (libc)File Positioning. * fseeko64: (libc)File Positioning. * fseeko: (libc)File Positioning. * fsetpos64: (libc)Portable Positioning. * fsetpos: (libc)Portable Positioning. * fsqrt: (libc)Misc FP Arithmetic. * fsqrtl: (libc)Misc FP Arithmetic. * fstat64: (libc)Reading Attributes. * fstat: (libc)Reading Attributes. * fsub: (libc)Misc FP Arithmetic. * fsubl: (libc)Misc FP Arithmetic. * fsync: (libc)Synchronizing I/O. * ftell: (libc)File Positioning. * ftello64: (libc)File Positioning. * ftello: (libc)File Positioning. * ftruncate64: (libc)File Size. * ftruncate: (libc)File Size. * ftrylockfile: (libc)Streams and Threads. * ftw64: (libc)Working with Directory Trees. * ftw: (libc)Working with Directory Trees. * funlockfile: (libc)Streams and Threads. * futimes: (libc)File Times. * fwide: (libc)Streams and I18N. * fwprintf: (libc)Formatted Output Functions. * fwrite: (libc)Block Input/Output. * fwrite_unlocked: (libc)Block Input/Output. * fwscanf: (libc)Formatted Input Functions. * gamma: (libc)Special Functions. * gammaf: (libc)Special Functions. * gammal: (libc)Special Functions. * gcvt: (libc)System V Number Conversion. * get_avphys_pages: (libc)Query Memory Parameters. * get_current_dir_name: (libc)Working Directory. * get_nprocs: (libc)Processor Resources. * get_nprocs_conf: (libc)Processor Resources. * get_phys_pages: (libc)Query Memory Parameters. * getauxval: (libc)Auxiliary Vector. * getc: (libc)Character Input. * getc_unlocked: (libc)Character Input. * getchar: (libc)Character Input. * getchar_unlocked: (libc)Character Input. * getcontext: (libc)System V contexts. * getcpu: (libc)CPU Affinity. * getcwd: (libc)Working Directory. * getdate: (libc)General Time String Parsing. * getdate_r: (libc)General Time String Parsing. * getdelim: (libc)Line Input. * getdents64: (libc)Low-level Directory Access. * getdomainnname: (libc)Host Identification. * getegid: (libc)Reading Persona. * getentropy: (libc)Unpredictable Bytes. * getenv: (libc)Environment Access. * geteuid: (libc)Reading Persona. * getfsent: (libc)fstab. * getfsfile: (libc)fstab. * getfsspec: (libc)fstab. * getgid: (libc)Reading Persona. * getgrent: (libc)Scanning All Groups. * getgrent_r: (libc)Scanning All Groups. * getgrgid: (libc)Lookup Group. * getgrgid_r: (libc)Lookup Group. * getgrnam: (libc)Lookup Group. * getgrnam_r: (libc)Lookup Group. * getgrouplist: (libc)Setting Groups. * getgroups: (libc)Reading Persona. * gethostbyaddr: (libc)Host Names. * gethostbyaddr_r: (libc)Host Names. * gethostbyname2: (libc)Host Names. * gethostbyname2_r: (libc)Host Names. * gethostbyname: (libc)Host Names. * gethostbyname_r: (libc)Host Names. * gethostent: (libc)Host Names. * gethostid: (libc)Host Identification. * gethostname: (libc)Host Identification. * getitimer: (libc)Setting an Alarm. * getline: (libc)Line Input. * getloadavg: (libc)Processor Resources. * getlogin: (libc)Who Logged In. * getmntent: (libc)mtab. * getmntent_r: (libc)mtab. * getnetbyaddr: (libc)Networks Database. * getnetbyname: (libc)Networks Database. * getnetent: (libc)Networks Database. * getnetgrent: (libc)Lookup Netgroup. * getnetgrent_r: (libc)Lookup Netgroup. * getopt: (libc)Using Getopt. * getopt_long: (libc)Getopt Long Options. * getopt_long_only: (libc)Getopt Long Options. * getpagesize: (libc)Query Memory Parameters. * getpass: (libc)getpass. * getpayload: (libc)FP Bit Twiddling. * getpayloadf: (libc)FP Bit Twiddling. * getpayloadfN: (libc)FP Bit Twiddling. * getpayloadfNx: (libc)FP Bit Twiddling. * getpayloadl: (libc)FP Bit Twiddling. * getpeername: (libc)Who is Connected. * getpgid: (libc)Process Group Functions. * getpgrp: (libc)Process Group Functions. * getpid: (libc)Process Identification. * getppid: (libc)Process Identification. * getpriority: (libc)Traditional Scheduling Functions. * getprotobyname: (libc)Protocols Database. * getprotobynumber: (libc)Protocols Database. * getprotoent: (libc)Protocols Database. * getpt: (libc)Allocation. * getpwent: (libc)Scanning All Users. * getpwent_r: (libc)Scanning All Users. * getpwnam: (libc)Lookup User. * getpwnam_r: (libc)Lookup User. * getpwuid: (libc)Lookup User. * getpwuid_r: (libc)Lookup User. * getrandom: (libc)Unpredictable Bytes. * getrlimit64: (libc)Limits on Resources. * getrlimit: (libc)Limits on Resources. * getrusage: (libc)Resource Usage. * gets: (libc)Line Input. * getservbyname: (libc)Services Database. * getservbyport: (libc)Services Database. * getservent: (libc)Services Database. * getsid: (libc)Process Group Functions. * getsockname: (libc)Reading Address. * getsockopt: (libc)Socket Option Functions. * getsubopt: (libc)Suboptions. * gettext: (libc)Translation with gettext. * gettid: (libc)Process Identification. * gettimeofday: (libc)Getting the Time. * getuid: (libc)Reading Persona. * getumask: (libc)Setting Permissions. * getutent: (libc)Manipulating the Database. * getutent_r: (libc)Manipulating the Database. * getutid: (libc)Manipulating the Database. * getutid_r: (libc)Manipulating the Database. * getutline: (libc)Manipulating the Database. * getutline_r: (libc)Manipulating the Database. * getutmp: (libc)XPG Functions. * getutmpx: (libc)XPG Functions. * getutxent: (libc)XPG Functions. * getutxid: (libc)XPG Functions. * getutxline: (libc)XPG Functions. * getw: (libc)Character Input. * getwc: (libc)Character Input. * getwc_unlocked: (libc)Character Input. * getwchar: (libc)Character Input. * getwchar_unlocked: (libc)Character Input. * getwd: (libc)Working Directory. * glob64: (libc)Calling Glob. * glob: (libc)Calling Glob. * globfree64: (libc)More Flags for Globbing. * globfree: (libc)More Flags for Globbing. * gmtime: (libc)Broken-down Time. * gmtime_r: (libc)Broken-down Time. * grantpt: (libc)Allocation. * gsignal: (libc)Signaling Yourself. * gtty: (libc)BSD Terminal Modes. * hasmntopt: (libc)mtab. * hcreate: (libc)Hash Search Function. * hcreate_r: (libc)Hash Search Function. * hdestroy: (libc)Hash Search Function. * hdestroy_r: (libc)Hash Search Function. * hsearch: (libc)Hash Search Function. * hsearch_r: (libc)Hash Search Function. * htonl: (libc)Byte Order. * htons: (libc)Byte Order. * hypot: (libc)Exponents and Logarithms. * hypotf: (libc)Exponents and Logarithms. * hypotfN: (libc)Exponents and Logarithms. * hypotfNx: (libc)Exponents and Logarithms. * hypotl: (libc)Exponents and Logarithms. * iconv: (libc)Generic Conversion Interface. * iconv_close: (libc)Generic Conversion Interface. * iconv_open: (libc)Generic Conversion Interface. * if_freenameindex: (libc)Interface Naming. * if_indextoname: (libc)Interface Naming. * if_nameindex: (libc)Interface Naming. * if_nametoindex: (libc)Interface Naming. * ilogb: (libc)Exponents and Logarithms. * ilogbf: (libc)Exponents and Logarithms. * ilogbfN: (libc)Exponents and Logarithms. * ilogbfNx: (libc)Exponents and Logarithms. * ilogbl: (libc)Exponents and Logarithms. * imaxabs: (libc)Absolute Value. * imaxdiv: (libc)Integer Division. * in6addr_any: (libc)Host Address Data Type. * in6addr_loopback: (libc)Host Address Data Type. * index: (libc)Search Functions. * inet_addr: (libc)Host Address Functions. * inet_aton: (libc)Host Address Functions. * inet_lnaof: (libc)Host Address Functions. * inet_makeaddr: (libc)Host Address Functions. * inet_netof: (libc)Host Address Functions. * inet_network: (libc)Host Address Functions. * inet_ntoa: (libc)Host Address Functions. * inet_ntop: (libc)Host Address Functions. * inet_pton: (libc)Host Address Functions. * initgroups: (libc)Setting Groups. * initstate: (libc)BSD Random. * initstate_r: (libc)BSD Random. * innetgr: (libc)Netgroup Membership. * ioctl: (libc)IOCTLs. * isalnum: (libc)Classification of Characters. * isalpha: (libc)Classification of Characters. * isascii: (libc)Classification of Characters. * isatty: (libc)Is It a Terminal. * isblank: (libc)Classification of Characters. * iscanonical: (libc)Floating Point Classes. * iscntrl: (libc)Classification of Characters. * isdigit: (libc)Classification of Characters. * iseqsig: (libc)FP Comparison Functions. * isfinite: (libc)Floating Point Classes. * isgraph: (libc)Classification of Characters. * isgreater: (libc)FP Comparison Functions. * isgreaterequal: (libc)FP Comparison Functions. * isinf: (libc)Floating Point Classes. * isinff: (libc)Floating Point Classes. * isinfl: (libc)Floating Point Classes. * isless: (libc)FP Comparison Functions. * islessequal: (libc)FP Comparison Functions. * islessgreater: (libc)FP Comparison Functions. * islower: (libc)Classification of Characters. * isnan: (libc)Floating Point Classes. * isnan: (libc)Floating Point Classes. * isnanf: (libc)Floating Point Classes. * isnanl: (libc)Floating Point Classes. * isnormal: (libc)Floating Point Classes. * isprint: (libc)Classification of Characters. * ispunct: (libc)Classification of Characters. * issignaling: (libc)Floating Point Classes. * isspace: (libc)Classification of Characters. * issubnormal: (libc)Floating Point Classes. * isunordered: (libc)FP Comparison Functions. * isupper: (libc)Classification of Characters. * iswalnum: (libc)Classification of Wide Characters. * iswalpha: (libc)Classification of Wide Characters. * iswblank: (libc)Classification of Wide Characters. * iswcntrl: (libc)Classification of Wide Characters. * iswctype: (libc)Classification of Wide Characters. * iswdigit: (libc)Classification of Wide Characters. * iswgraph: (libc)Classification of Wide Characters. * iswlower: (libc)Classification of Wide Characters. * iswprint: (libc)Classification of Wide Characters. * iswpunct: (libc)Classification of Wide Characters. * iswspace: (libc)Classification of Wide Characters. * iswupper: (libc)Classification of Wide Characters. * iswxdigit: (libc)Classification of Wide Characters. * isxdigit: (libc)Classification of Characters. * iszero: (libc)Floating Point Classes. * j0: (libc)Special Functions. * j0f: (libc)Special Functions. * j0fN: (libc)Special Functions. * j0fNx: (libc)Special Functions. * j0l: (libc)Special Functions. * j1: (libc)Special Functions. * j1f: (libc)Special Functions. * j1fN: (libc)Special Functions. * j1fNx: (libc)Special Functions. * j1l: (libc)Special Functions. * jn: (libc)Special Functions. * jnf: (libc)Special Functions. * jnfN: (libc)Special Functions. * jnfNx: (libc)Special Functions. * jnl: (libc)Special Functions. * jrand48: (libc)SVID Random. * jrand48_r: (libc)SVID Random. * kill: (libc)Signaling Another Process. * killpg: (libc)Signaling Another Process. * l64a: (libc)Encode Binary Data. * labs: (libc)Absolute Value. * lcong48: (libc)SVID Random. * lcong48_r: (libc)SVID Random. * ldexp: (libc)Normalization Functions. * ldexpf: (libc)Normalization Functions. * ldexpfN: (libc)Normalization Functions. * ldexpfNx: (libc)Normalization Functions. * ldexpl: (libc)Normalization Functions. * ldiv: (libc)Integer Division. * lfind: (libc)Array Search Function. * lgamma: (libc)Special Functions. * lgamma_r: (libc)Special Functions. * lgammaf: (libc)Special Functions. * lgammafN: (libc)Special Functions. * lgammafN_r: (libc)Special Functions. * lgammafNx: (libc)Special Functions. * lgammafNx_r: (libc)Special Functions. * lgammaf_r: (libc)Special Functions. * lgammal: (libc)Special Functions. * lgammal_r: (libc)Special Functions. * link: (libc)Hard Links. * linkat: (libc)Hard Links. * lio_listio64: (libc)Asynchronous Reads/Writes. * lio_listio: (libc)Asynchronous Reads/Writes. * listen: (libc)Listening. * llabs: (libc)Absolute Value. * lldiv: (libc)Integer Division. * llogb: (libc)Exponents and Logarithms. * llogbf: (libc)Exponents and Logarithms. * llogbfN: (libc)Exponents and Logarithms. * llogbfNx: (libc)Exponents and Logarithms. * llogbl: (libc)Exponents and Logarithms. * llrint: (libc)Rounding Functions. * llrintf: (libc)Rounding Functions. * llrintfN: (libc)Rounding Functions. * llrintfNx: (libc)Rounding Functions. * llrintl: (libc)Rounding Functions. * llround: (libc)Rounding Functions. * llroundf: (libc)Rounding Functions. * llroundfN: (libc)Rounding Functions. * llroundfNx: (libc)Rounding Functions. * llroundl: (libc)Rounding Functions. * localeconv: (libc)The Lame Way to Locale Data. * localtime: (libc)Broken-down Time. * localtime_r: (libc)Broken-down Time. * log10: (libc)Exponents and Logarithms. * log10f: (libc)Exponents and Logarithms. * log10fN: (libc)Exponents and Logarithms. * log10fNx: (libc)Exponents and Logarithms. * log10l: (libc)Exponents and Logarithms. * log1p: (libc)Exponents and Logarithms. * log1pf: (libc)Exponents and Logarithms. * log1pfN: (libc)Exponents and Logarithms. * log1pfNx: (libc)Exponents and Logarithms. * log1pl: (libc)Exponents and Logarithms. * log2: (libc)Exponents and Logarithms. * log2f: (libc)Exponents and Logarithms. * log2fN: (libc)Exponents and Logarithms. * log2fNx: (libc)Exponents and Logarithms. * log2l: (libc)Exponents and Logarithms. * log: (libc)Exponents and Logarithms. * logb: (libc)Exponents and Logarithms. * logbf: (libc)Exponents and Logarithms. * logbfN: (libc)Exponents and Logarithms. * logbfNx: (libc)Exponents and Logarithms. * logbl: (libc)Exponents and Logarithms. * logf: (libc)Exponents and Logarithms. * logfN: (libc)Exponents and Logarithms. * logfNx: (libc)Exponents and Logarithms. * login: (libc)Logging In and Out. * login_tty: (libc)Logging In and Out. * logl: (libc)Exponents and Logarithms. * logout: (libc)Logging In and Out. * logwtmp: (libc)Logging In and Out. * longjmp: (libc)Non-Local Details. * lrand48: (libc)SVID Random. * lrand48_r: (libc)SVID Random. * lrint: (libc)Rounding Functions. * lrintf: (libc)Rounding Functions. * lrintfN: (libc)Rounding Functions. * lrintfNx: (libc)Rounding Functions. * lrintl: (libc)Rounding Functions. * lround: (libc)Rounding Functions. * lroundf: (libc)Rounding Functions. * lroundfN: (libc)Rounding Functions. * lroundfNx: (libc)Rounding Functions. * lroundl: (libc)Rounding Functions. * lsearch: (libc)Array Search Function. * lseek64: (libc)File Position Primitive. * lseek: (libc)File Position Primitive. * lstat64: (libc)Reading Attributes. * lstat: (libc)Reading Attributes. * lutimes: (libc)File Times. * madvise: (libc)Memory-mapped I/O. * makecontext: (libc)System V contexts. * mallinfo2: (libc)Statistics of Malloc. * malloc: (libc)Basic Allocation. * mallopt: (libc)Malloc Tunable Parameters. * mblen: (libc)Non-reentrant Character Conversion. * mbrlen: (libc)Converting a Character. * mbrtowc: (libc)Converting a Character. * mbsinit: (libc)Keeping the state. * mbsnrtowcs: (libc)Converting Strings. * mbsrtowcs: (libc)Converting Strings. * mbstowcs: (libc)Non-reentrant String Conversion. * mbtowc: (libc)Non-reentrant Character Conversion. * mcheck: (libc)Heap Consistency Checking. * memalign: (libc)Aligned Memory Blocks. * memccpy: (libc)Copying Strings and Arrays. * memchr: (libc)Search Functions. * memcmp: (libc)String/Array Comparison. * memcpy: (libc)Copying Strings and Arrays. * memfd_create: (libc)Memory-mapped I/O. * memfrob: (libc)Obfuscating Data. * memmem: (libc)Search Functions. * memmove: (libc)Copying Strings and Arrays. * mempcpy: (libc)Copying Strings and Arrays. * memrchr: (libc)Search Functions. * memset: (libc)Copying Strings and Arrays. * mkdir: (libc)Creating Directories. * mkdtemp: (libc)Temporary Files. * mkfifo: (libc)FIFO Special Files. * mknod: (libc)Making Special Files. * mkstemp: (libc)Temporary Files. * mktemp: (libc)Temporary Files. * mktime: (libc)Broken-down Time. * mlock2: (libc)Page Lock Functions. * mlock: (libc)Page Lock Functions. * mlockall: (libc)Page Lock Functions. * mmap64: (libc)Memory-mapped I/O. * mmap: (libc)Memory-mapped I/O. * modf: (libc)Rounding Functions. * modff: (libc)Rounding Functions. * modffN: (libc)Rounding Functions. * modffNx: (libc)Rounding Functions. * modfl: (libc)Rounding Functions. * mount: (libc)Mount-Unmount-Remount. * mprobe: (libc)Heap Consistency Checking. * mprotect: (libc)Memory Protection. * mrand48: (libc)SVID Random. * mrand48_r: (libc)SVID Random. * mremap: (libc)Memory-mapped I/O. * msync: (libc)Memory-mapped I/O. * mtrace: (libc)Tracing malloc. * mtx_destroy: (libc)ISO C Mutexes. * mtx_init: (libc)ISO C Mutexes. * mtx_lock: (libc)ISO C Mutexes. * mtx_timedlock: (libc)ISO C Mutexes. * mtx_trylock: (libc)ISO C Mutexes. * mtx_unlock: (libc)ISO C Mutexes. * munlock: (libc)Page Lock Functions. * munlockall: (libc)Page Lock Functions. * munmap: (libc)Memory-mapped I/O. * muntrace: (libc)Tracing malloc. * nan: (libc)FP Bit Twiddling. * nanf: (libc)FP Bit Twiddling. * nanfN: (libc)FP Bit Twiddling. * nanfNx: (libc)FP Bit Twiddling. * nanl: (libc)FP Bit Twiddling. * nanosleep: (libc)Sleeping. * nearbyint: (libc)Rounding Functions. * nearbyintf: (libc)Rounding Functions. * nearbyintfN: (libc)Rounding Functions. * nearbyintfNx: (libc)Rounding Functions. * nearbyintl: (libc)Rounding Functions. * nextafter: (libc)FP Bit Twiddling. * nextafterf: (libc)FP Bit Twiddling. * nextafterfN: (libc)FP Bit Twiddling. * nextafterfNx: (libc)FP Bit Twiddling. * nextafterl: (libc)FP Bit Twiddling. * nextdown: (libc)FP Bit Twiddling. * nextdownf: (libc)FP Bit Twiddling. * nextdownfN: (libc)FP Bit Twiddling. * nextdownfNx: (libc)FP Bit Twiddling. * nextdownl: (libc)FP Bit Twiddling. * nexttoward: (libc)FP Bit Twiddling. * nexttowardf: (libc)FP Bit Twiddling. * nexttowardl: (libc)FP Bit Twiddling. * nextup: (libc)FP Bit Twiddling. * nextupf: (libc)FP Bit Twiddling. * nextupfN: (libc)FP Bit Twiddling. * nextupfNx: (libc)FP Bit Twiddling. * nextupl: (libc)FP Bit Twiddling. * nftw64: (libc)Working with Directory Trees. * nftw: (libc)Working with Directory Trees. * ngettext: (libc)Advanced gettext functions. * nice: (libc)Traditional Scheduling Functions. * nl_langinfo: (libc)The Elegant and Fast Way. * nrand48: (libc)SVID Random. * nrand48_r: (libc)SVID Random. * ntohl: (libc)Byte Order. * ntohs: (libc)Byte Order. * ntp_adjtime: (libc)Setting and Adjusting the Time. * ntp_gettime: (libc)Setting and Adjusting the Time. * obstack_1grow: (libc)Growing Objects. * obstack_1grow_fast: (libc)Extra Fast Growing. * obstack_alignment_mask: (libc)Obstacks Data Alignment. * obstack_alloc: (libc)Allocation in an Obstack. * obstack_base: (libc)Status of an Obstack. * obstack_blank: (libc)Growing Objects. * obstack_blank_fast: (libc)Extra Fast Growing. * obstack_chunk_size: (libc)Obstack Chunks. * obstack_copy0: (libc)Allocation in an Obstack. * obstack_copy: (libc)Allocation in an Obstack. * obstack_finish: (libc)Growing Objects. * obstack_free: (libc)Freeing Obstack Objects. * obstack_grow0: (libc)Growing Objects. * obstack_grow: (libc)Growing Objects. * obstack_init: (libc)Preparing for Obstacks. * obstack_int_grow: (libc)Growing Objects. * obstack_int_grow_fast: (libc)Extra Fast Growing. * obstack_next_free: (libc)Status of an Obstack. * obstack_object_size: (libc)Growing Objects. * obstack_object_size: (libc)Status of an Obstack. * obstack_printf: (libc)Dynamic Output. * obstack_ptr_grow: (libc)Growing Objects. * obstack_ptr_grow_fast: (libc)Extra Fast Growing. * obstack_room: (libc)Extra Fast Growing. * obstack_vprintf: (libc)Variable Arguments Output. * offsetof: (libc)Structure Measurement. * on_exit: (libc)Cleanups on Exit. * open64: (libc)Opening and Closing Files. * open: (libc)Opening and Closing Files. * open_memstream: (libc)String Streams. * opendir: (libc)Opening a Directory. * openlog: (libc)openlog. * openpty: (libc)Pseudo-Terminal Pairs. * parse_printf_format: (libc)Parsing a Template String. * pathconf: (libc)Pathconf. * pause: (libc)Using Pause. * pclose: (libc)Pipe to a Subprocess. * perror: (libc)Error Messages. * pipe: (libc)Creating a Pipe. * pkey_alloc: (libc)Memory Protection. * pkey_free: (libc)Memory Protection. * pkey_get: (libc)Memory Protection. * pkey_mprotect: (libc)Memory Protection. * pkey_set: (libc)Memory Protection. * popen: (libc)Pipe to a Subprocess. * posix_fallocate64: (libc)Storage Allocation. * posix_fallocate: (libc)Storage Allocation. * posix_memalign: (libc)Aligned Memory Blocks. * pow: (libc)Exponents and Logarithms. * powf: (libc)Exponents and Logarithms. * powfN: (libc)Exponents and Logarithms. * powfNx: (libc)Exponents and Logarithms. * powl: (libc)Exponents and Logarithms. * pread64: (libc)I/O Primitives. * pread: (libc)I/O Primitives. * preadv2: (libc)Scatter-Gather. * preadv64: (libc)Scatter-Gather. * preadv64v2: (libc)Scatter-Gather. * preadv: (libc)Scatter-Gather. * printf: (libc)Formatted Output Functions. * printf_size: (libc)Predefined Printf Handlers. * printf_size_info: (libc)Predefined Printf Handlers. * psignal: (libc)Signal Messages. * pthread_attr_getsigmask_np: (libc)Initial Thread Signal Mask. * pthread_attr_setsigmask_np: (libc)Initial Thread Signal Mask. * pthread_clockjoin_np: (libc)Waiting with Explicit Clocks. * pthread_cond_clockwait: (libc)Waiting with Explicit Clocks. * pthread_getattr_default_np: (libc)Default Thread Attributes. * pthread_getspecific: (libc)Thread-specific Data. * pthread_key_create: (libc)Thread-specific Data. * pthread_key_delete: (libc)Thread-specific Data. * pthread_rwlock_clockrdlock: (libc)Waiting with Explicit Clocks. * pthread_rwlock_clockwrlock: (libc)Waiting with Explicit Clocks. * pthread_setattr_default_np: (libc)Default Thread Attributes. * pthread_setspecific: (libc)Thread-specific Data. * pthread_timedjoin_np: (libc)Waiting with Explicit Clocks. * pthread_tryjoin_np: (libc)Waiting with Explicit Clocks. * ptsname: (libc)Allocation. * ptsname_r: (libc)Allocation. * putc: (libc)Simple Output. * putc_unlocked: (libc)Simple Output. * putchar: (libc)Simple Output. * putchar_unlocked: (libc)Simple Output. * putenv: (libc)Environment Access. * putpwent: (libc)Writing a User Entry. * puts: (libc)Simple Output. * pututline: (libc)Manipulating the Database. * pututxline: (libc)XPG Functions. * putw: (libc)Simple Output. * putwc: (libc)Simple Output. * putwc_unlocked: (libc)Simple Output. * putwchar: (libc)Simple Output. * putwchar_unlocked: (libc)Simple Output. * pwrite64: (libc)I/O Primitives. * pwrite: (libc)I/O Primitives. * pwritev2: (libc)Scatter-Gather. * pwritev64: (libc)Scatter-Gather. * pwritev64v2: (libc)Scatter-Gather. * pwritev: (libc)Scatter-Gather. * qecvt: (libc)System V Number Conversion. * qecvt_r: (libc)System V Number Conversion. * qfcvt: (libc)System V Number Conversion. * qfcvt_r: (libc)System V Number Conversion. * qgcvt: (libc)System V Number Conversion. * qsort: (libc)Array Sort Function. * raise: (libc)Signaling Yourself. * rand: (libc)ISO Random. * rand_r: (libc)ISO Random. * random: (libc)BSD Random. * random_r: (libc)BSD Random. * rawmemchr: (libc)Search Functions. * read: (libc)I/O Primitives. * readdir64: (libc)Reading/Closing Directory. * readdir64_r: (libc)Reading/Closing Directory. * readdir: (libc)Reading/Closing Directory. * readdir_r: (libc)Reading/Closing Directory. * readlink: (libc)Symbolic Links. * readv: (libc)Scatter-Gather. * realloc: (libc)Changing Block Size. * reallocarray: (libc)Changing Block Size. * realpath: (libc)Symbolic Links. * recv: (libc)Receiving Data. * recvfrom: (libc)Receiving Datagrams. * recvmsg: (libc)Receiving Datagrams. * regcomp: (libc)POSIX Regexp Compilation. * regerror: (libc)Regexp Cleanup. * regexec: (libc)Matching POSIX Regexps. * regfree: (libc)Regexp Cleanup. * register_printf_function: (libc)Registering New Conversions. * remainder: (libc)Remainder Functions. * remainderf: (libc)Remainder Functions. * remainderfN: (libc)Remainder Functions. * remainderfNx: (libc)Remainder Functions. * remainderl: (libc)Remainder Functions. * remove: (libc)Deleting Files. * rename: (libc)Renaming Files. * rewind: (libc)File Positioning. * rewinddir: (libc)Random Access Directory. * rindex: (libc)Search Functions. * rint: (libc)Rounding Functions. * rintf: (libc)Rounding Functions. * rintfN: (libc)Rounding Functions. * rintfNx: (libc)Rounding Functions. * rintl: (libc)Rounding Functions. * rmdir: (libc)Deleting Files. * round: (libc)Rounding Functions. * roundeven: (libc)Rounding Functions. * roundevenf: (libc)Rounding Functions. * roundevenfN: (libc)Rounding Functions. * roundevenfNx: (libc)Rounding Functions. * roundevenl: (libc)Rounding Functions. * roundf: (libc)Rounding Functions. * roundfN: (libc)Rounding Functions. * roundfNx: (libc)Rounding Functions. * roundl: (libc)Rounding Functions. * rpmatch: (libc)Yes-or-No Questions. * sbrk: (libc)Resizing the Data Segment. * scalb: (libc)Normalization Functions. * scalbf: (libc)Normalization Functions. * scalbl: (libc)Normalization Functions. * scalbln: (libc)Normalization Functions. * scalblnf: (libc)Normalization Functions. * scalblnfN: (libc)Normalization Functions. * scalblnfNx: (libc)Normalization Functions. * scalblnl: (libc)Normalization Functions. * scalbn: (libc)Normalization Functions. * scalbnf: (libc)Normalization Functions. * scalbnfN: (libc)Normalization Functions. * scalbnfNx: (libc)Normalization Functions. * scalbnl: (libc)Normalization Functions. * scandir64: (libc)Scanning Directory Content. * scandir: (libc)Scanning Directory Content. * scanf: (libc)Formatted Input Functions. * sched_get_priority_max: (libc)Basic Scheduling Functions. * sched_get_priority_min: (libc)Basic Scheduling Functions. * sched_getaffinity: (libc)CPU Affinity. * sched_getparam: (libc)Basic Scheduling Functions. * sched_getscheduler: (libc)Basic Scheduling Functions. * sched_rr_get_interval: (libc)Basic Scheduling Functions. * sched_setaffinity: (libc)CPU Affinity. * sched_setparam: (libc)Basic Scheduling Functions. * sched_setscheduler: (libc)Basic Scheduling Functions. * sched_yield: (libc)Basic Scheduling Functions. * secure_getenv: (libc)Environment Access. * seed48: (libc)SVID Random. * seed48_r: (libc)SVID Random. * seekdir: (libc)Random Access Directory. * select: (libc)Waiting for I/O. * sem_clockwait: (libc)Waiting with Explicit Clocks. * sem_close: (libc)Semaphores. * sem_destroy: (libc)Semaphores. * sem_getvalue: (libc)Semaphores. * sem_init: (libc)Semaphores. * sem_open: (libc)Semaphores. * sem_post: (libc)Semaphores. * sem_timedwait: (libc)Semaphores. * sem_trywait: (libc)Semaphores. * sem_unlink: (libc)Semaphores. * sem_wait: (libc)Semaphores. * semctl: (libc)Semaphores. * semget: (libc)Semaphores. * semop: (libc)Semaphores. * semtimedop: (libc)Semaphores. * send: (libc)Sending Data. * sendmsg: (libc)Receiving Datagrams. * sendto: (libc)Sending Datagrams. * setbuf: (libc)Controlling Buffering. * setbuffer: (libc)Controlling Buffering. * setcontext: (libc)System V contexts. * setdomainname: (libc)Host Identification. * setegid: (libc)Setting Groups. * setenv: (libc)Environment Access. * seteuid: (libc)Setting User ID. * setfsent: (libc)fstab. * setgid: (libc)Setting Groups. * setgrent: (libc)Scanning All Groups. * setgroups: (libc)Setting Groups. * sethostent: (libc)Host Names. * sethostid: (libc)Host Identification. * sethostname: (libc)Host Identification. * setitimer: (libc)Setting an Alarm. * setjmp: (libc)Non-Local Details. * setlinebuf: (libc)Controlling Buffering. * setlocale: (libc)Setting the Locale. * setlogmask: (libc)setlogmask. * setmntent: (libc)mtab. * setnetent: (libc)Networks Database. * setnetgrent: (libc)Lookup Netgroup. * setpayload: (libc)FP Bit Twiddling. * setpayloadf: (libc)FP Bit Twiddling. * setpayloadfN: (libc)FP Bit Twiddling. * setpayloadfNx: (libc)FP Bit Twiddling. * setpayloadl: (libc)FP Bit Twiddling. * setpayloadsig: (libc)FP Bit Twiddling. * setpayloadsigf: (libc)FP Bit Twiddling. * setpayloadsigfN: (libc)FP Bit Twiddling. * setpayloadsigfNx: (libc)FP Bit Twiddling. * setpayloadsigl: (libc)FP Bit Twiddling. * setpgid: (libc)Process Group Functions. * setpgrp: (libc)Process Group Functions. * setpriority: (libc)Traditional Scheduling Functions. * setprotoent: (libc)Protocols Database. * setpwent: (libc)Scanning All Users. * setregid: (libc)Setting Groups. * setreuid: (libc)Setting User ID. * setrlimit64: (libc)Limits on Resources. * setrlimit: (libc)Limits on Resources. * setservent: (libc)Services Database. * setsid: (libc)Process Group Functions. * setsockopt: (libc)Socket Option Functions. * setstate: (libc)BSD Random. * setstate_r: (libc)BSD Random. * settimeofday: (libc)Setting and Adjusting the Time. * setuid: (libc)Setting User ID. * setutent: (libc)Manipulating the Database. * setutxent: (libc)XPG Functions. * setvbuf: (libc)Controlling Buffering. * shm_open: (libc)Memory-mapped I/O. * shm_unlink: (libc)Memory-mapped I/O. * shutdown: (libc)Closing a Socket. * sigabbrev_np: (libc)Signal Messages. * sigaction: (libc)Advanced Signal Handling. * sigaddset: (libc)Signal Sets. * sigaltstack: (libc)Signal Stack. * sigblock: (libc)BSD Signal Handling. * sigdelset: (libc)Signal Sets. * sigdescr_np: (libc)Signal Messages. * sigemptyset: (libc)Signal Sets. * sigfillset: (libc)Signal Sets. * siginterrupt: (libc)BSD Signal Handling. * sigismember: (libc)Signal Sets. * siglongjmp: (libc)Non-Local Exits and Signals. * sigmask: (libc)BSD Signal Handling. * signal: (libc)Basic Signal Handling. * signbit: (libc)FP Bit Twiddling. * significand: (libc)Normalization Functions. * significandf: (libc)Normalization Functions. * significandl: (libc)Normalization Functions. * sigpause: (libc)BSD Signal Handling. * sigpending: (libc)Checking for Pending Signals. * sigprocmask: (libc)Process Signal Mask. * sigsetjmp: (libc)Non-Local Exits and Signals. * sigsetmask: (libc)BSD Signal Handling. * sigstack: (libc)Signal Stack. * sigsuspend: (libc)Sigsuspend. * sin: (libc)Trig Functions. * sincos: (libc)Trig Functions. * sincosf: (libc)Trig Functions. * sincosfN: (libc)Trig Functions. * sincosfNx: (libc)Trig Functions. * sincosl: (libc)Trig Functions. * sinf: (libc)Trig Functions. * sinfN: (libc)Trig Functions. * sinfNx: (libc)Trig Functions. * sinh: (libc)Hyperbolic Functions. * sinhf: (libc)Hyperbolic Functions. * sinhfN: (libc)Hyperbolic Functions. * sinhfNx: (libc)Hyperbolic Functions. * sinhl: (libc)Hyperbolic Functions. * sinl: (libc)Trig Functions. * sleep: (libc)Sleeping. * snprintf: (libc)Formatted Output Functions. * socket: (libc)Creating a Socket. * socketpair: (libc)Socket Pairs. * sprintf: (libc)Formatted Output Functions. * sqrt: (libc)Exponents and Logarithms. * sqrtf: (libc)Exponents and Logarithms. * sqrtfN: (libc)Exponents and Logarithms. * sqrtfNx: (libc)Exponents and Logarithms. * sqrtl: (libc)Exponents and Logarithms. * srand48: (libc)SVID Random. * srand48_r: (libc)SVID Random. * srand: (libc)ISO Random. * srandom: (libc)BSD Random. * srandom_r: (libc)BSD Random. * sscanf: (libc)Formatted Input Functions. * ssignal: (libc)Basic Signal Handling. * stat64: (libc)Reading Attributes. * stat: (libc)Reading Attributes. * stime: (libc)Setting and Adjusting the Time. * stpcpy: (libc)Copying Strings and Arrays. * stpncpy: (libc)Truncating Strings. * strcasecmp: (libc)String/Array Comparison. * strcasestr: (libc)Search Functions. * strcat: (libc)Concatenating Strings. * strchr: (libc)Search Functions. * strchrnul: (libc)Search Functions. * strcmp: (libc)String/Array Comparison. * strcoll: (libc)Collation Functions. * strcpy: (libc)Copying Strings and Arrays. * strcspn: (libc)Search Functions. * strdup: (libc)Copying Strings and Arrays. * strdupa: (libc)Copying Strings and Arrays. * strerror: (libc)Error Messages. * strerror_r: (libc)Error Messages. * strerrordesc_np: (libc)Error Messages. * strerrorname_np: (libc)Error Messages. * strfmon: (libc)Formatting Numbers. * strfromd: (libc)Printing of Floats. * strfromf: (libc)Printing of Floats. * strfromfN: (libc)Printing of Floats. * strfromfNx: (libc)Printing of Floats. * strfroml: (libc)Printing of Floats. * strfry: (libc)Shuffling Bytes. * strftime: (libc)Formatting Calendar Time. * strlen: (libc)String Length. * strncasecmp: (libc)String/Array Comparison. * strncat: (libc)Truncating Strings. * strncmp: (libc)String/Array Comparison. * strncpy: (libc)Truncating Strings. * strndup: (libc)Truncating Strings. * strndupa: (libc)Truncating Strings. * strnlen: (libc)String Length. * strpbrk: (libc)Search Functions. * strptime: (libc)Low-Level Time String Parsing. * strrchr: (libc)Search Functions. * strsep: (libc)Finding Tokens in a String. * strsignal: (libc)Signal Messages. * strspn: (libc)Search Functions. * strstr: (libc)Search Functions. * strtod: (libc)Parsing of Floats. * strtof: (libc)Parsing of Floats. * strtofN: (libc)Parsing of Floats. * strtofNx: (libc)Parsing of Floats. * strtoimax: (libc)Parsing of Integers. * strtok: (libc)Finding Tokens in a String. * strtok_r: (libc)Finding Tokens in a String. * strtol: (libc)Parsing of Integers. * strtold: (libc)Parsing of Floats. * strtoll: (libc)Parsing of Integers. * strtoq: (libc)Parsing of Integers. * strtoul: (libc)Parsing of Integers. * strtoull: (libc)Parsing of Integers. * strtoumax: (libc)Parsing of Integers. * strtouq: (libc)Parsing of Integers. * strverscmp: (libc)String/Array Comparison. * strxfrm: (libc)Collation Functions. * stty: (libc)BSD Terminal Modes. * swapcontext: (libc)System V contexts. * swprintf: (libc)Formatted Output Functions. * swscanf: (libc)Formatted Input Functions. * symlink: (libc)Symbolic Links. * sync: (libc)Synchronizing I/O. * syscall: (libc)System Calls. * sysconf: (libc)Sysconf Definition. * syslog: (libc)syslog; vsyslog. * system: (libc)Running a Command. * sysv_signal: (libc)Basic Signal Handling. * tan: (libc)Trig Functions. * tanf: (libc)Trig Functions. * tanfN: (libc)Trig Functions. * tanfNx: (libc)Trig Functions. * tanh: (libc)Hyperbolic Functions. * tanhf: (libc)Hyperbolic Functions. * tanhfN: (libc)Hyperbolic Functions. * tanhfNx: (libc)Hyperbolic Functions. * tanhl: (libc)Hyperbolic Functions. * tanl: (libc)Trig Functions. * tcdrain: (libc)Line Control. * tcflow: (libc)Line Control. * tcflush: (libc)Line Control. * tcgetattr: (libc)Mode Functions. * tcgetpgrp: (libc)Terminal Access Functions. * tcgetsid: (libc)Terminal Access Functions. * tcsendbreak: (libc)Line Control. * tcsetattr: (libc)Mode Functions. * tcsetpgrp: (libc)Terminal Access Functions. * tdelete: (libc)Tree Search Function. * tdestroy: (libc)Tree Search Function. * telldir: (libc)Random Access Directory. * tempnam: (libc)Temporary Files. * textdomain: (libc)Locating gettext catalog. * tfind: (libc)Tree Search Function. * tgamma: (libc)Special Functions. * tgammaf: (libc)Special Functions. * tgammafN: (libc)Special Functions. * tgammafNx: (libc)Special Functions. * tgammal: (libc)Special Functions. * tgkill: (libc)Signaling Another Process. * thrd_create: (libc)ISO C Thread Management. * thrd_current: (libc)ISO C Thread Management. * thrd_detach: (libc)ISO C Thread Management. * thrd_equal: (libc)ISO C Thread Management. * thrd_exit: (libc)ISO C Thread Management. * thrd_join: (libc)ISO C Thread Management. * thrd_sleep: (libc)ISO C Thread Management. * thrd_yield: (libc)ISO C Thread Management. * time: (libc)Getting the Time. * timegm: (libc)Broken-down Time. * timelocal: (libc)Broken-down Time. * times: (libc)Processor Time. * tmpfile64: (libc)Temporary Files. * tmpfile: (libc)Temporary Files. * tmpnam: (libc)Temporary Files. * tmpnam_r: (libc)Temporary Files. * toascii: (libc)Case Conversion. * tolower: (libc)Case Conversion. * totalorder: (libc)FP Comparison Functions. * totalorderf: (libc)FP Comparison Functions. * totalorderfN: (libc)FP Comparison Functions. * totalorderfNx: (libc)FP Comparison Functions. * totalorderl: (libc)FP Comparison Functions. * totalordermag: (libc)FP Comparison Functions. * totalordermagf: (libc)FP Comparison Functions. * totalordermagfN: (libc)FP Comparison Functions. * totalordermagfNx: (libc)FP Comparison Functions. * totalordermagl: (libc)FP Comparison Functions. * toupper: (libc)Case Conversion. * towctrans: (libc)Wide Character Case Conversion. * towlower: (libc)Wide Character Case Conversion. * towupper: (libc)Wide Character Case Conversion. * trunc: (libc)Rounding Functions. * truncate64: (libc)File Size. * truncate: (libc)File Size. * truncf: (libc)Rounding Functions. * truncfN: (libc)Rounding Functions. * truncfNx: (libc)Rounding Functions. * truncl: (libc)Rounding Functions. * tsearch: (libc)Tree Search Function. * tss_create: (libc)ISO C Thread-local Storage. * tss_delete: (libc)ISO C Thread-local Storage. * tss_get: (libc)ISO C Thread-local Storage. * tss_set: (libc)ISO C Thread-local Storage. * ttyname: (libc)Is It a Terminal. * ttyname_r: (libc)Is It a Terminal. * twalk: (libc)Tree Search Function. * twalk_r: (libc)Tree Search Function. * tzset: (libc)Time Zone Functions. * ufromfp: (libc)Rounding Functions. * ufromfpf: (libc)Rounding Functions. * ufromfpfN: (libc)Rounding Functions. * ufromfpfNx: (libc)Rounding Functions. * ufromfpl: (libc)Rounding Functions. * ufromfpx: (libc)Rounding Functions. * ufromfpxf: (libc)Rounding Functions. * ufromfpxfN: (libc)Rounding Functions. * ufromfpxfNx: (libc)Rounding Functions. * ufromfpxl: (libc)Rounding Functions. * ulimit: (libc)Limits on Resources. * umask: (libc)Setting Permissions. * umount2: (libc)Mount-Unmount-Remount. * umount: (libc)Mount-Unmount-Remount. * uname: (libc)Platform Type. * ungetc: (libc)How Unread. * ungetwc: (libc)How Unread. * unlink: (libc)Deleting Files. * unlockpt: (libc)Allocation. * unsetenv: (libc)Environment Access. * updwtmp: (libc)Manipulating the Database. * utime: (libc)File Times. * utimes: (libc)File Times. * utmpname: (libc)Manipulating the Database. * utmpxname: (libc)XPG Functions. * va_arg: (libc)Argument Macros. * va_copy: (libc)Argument Macros. * va_end: (libc)Argument Macros. * va_start: (libc)Argument Macros. * valloc: (libc)Aligned Memory Blocks. * vasprintf: (libc)Variable Arguments Output. * verr: (libc)Error Messages. * verrx: (libc)Error Messages. * versionsort64: (libc)Scanning Directory Content. * versionsort: (libc)Scanning Directory Content. * vfork: (libc)Creating a Process. * vfprintf: (libc)Variable Arguments Output. * vfscanf: (libc)Variable Arguments Input. * vfwprintf: (libc)Variable Arguments Output. * vfwscanf: (libc)Variable Arguments Input. * vlimit: (libc)Limits on Resources. * vprintf: (libc)Variable Arguments Output. * vscanf: (libc)Variable Arguments Input. * vsnprintf: (libc)Variable Arguments Output. * vsprintf: (libc)Variable Arguments Output. * vsscanf: (libc)Variable Arguments Input. * vswprintf: (libc)Variable Arguments Output. * vswscanf: (libc)Variable Arguments Input. * vsyslog: (libc)syslog; vsyslog. * vwarn: (libc)Error Messages. * vwarnx: (libc)Error Messages. * vwprintf: (libc)Variable Arguments Output. * vwscanf: (libc)Variable Arguments Input. * wait3: (libc)BSD Wait Functions. * wait4: (libc)Process Completion. * wait: (libc)Process Completion. * waitpid: (libc)Process Completion. * warn: (libc)Error Messages. * warnx: (libc)Error Messages. * wcpcpy: (libc)Copying Strings and Arrays. * wcpncpy: (libc)Truncating Strings. * wcrtomb: (libc)Converting a Character. * wcscasecmp: (libc)String/Array Comparison. * wcscat: (libc)Concatenating Strings. * wcschr: (libc)Search Functions. * wcschrnul: (libc)Search Functions. * wcscmp: (libc)String/Array Comparison. * wcscoll: (libc)Collation Functions. * wcscpy: (libc)Copying Strings and Arrays. * wcscspn: (libc)Search Functions. * wcsdup: (libc)Copying Strings and Arrays. * wcsftime: (libc)Formatting Calendar Time. * wcslen: (libc)String Length. * wcsncasecmp: (libc)String/Array Comparison. * wcsncat: (libc)Truncating Strings. * wcsncmp: (libc)String/Array Comparison. * wcsncpy: (libc)Truncating Strings. * wcsnlen: (libc)String Length. * wcsnrtombs: (libc)Converting Strings. * wcspbrk: (libc)Search Functions. * wcsrchr: (libc)Search Functions. * wcsrtombs: (libc)Converting Strings. * wcsspn: (libc)Search Functions. * wcsstr: (libc)Search Functions. * wcstod: (libc)Parsing of Floats. * wcstof: (libc)Parsing of Floats. * wcstofN: (libc)Parsing of Floats. * wcstofNx: (libc)Parsing of Floats. * wcstoimax: (libc)Parsing of Integers. * wcstok: (libc)Finding Tokens in a String. * wcstol: (libc)Parsing of Integers. * wcstold: (libc)Parsing of Floats. * wcstoll: (libc)Parsing of Integers. * wcstombs: (libc)Non-reentrant String Conversion. * wcstoq: (libc)Parsing of Integers. * wcstoul: (libc)Parsing of Integers. * wcstoull: (libc)Parsing of Integers. * wcstoumax: (libc)Parsing of Integers. * wcstouq: (libc)Parsing of Integers. * wcswcs: (libc)Search Functions. * wcsxfrm: (libc)Collation Functions. * wctob: (libc)Converting a Character. * wctomb: (libc)Non-reentrant Character Conversion. * wctrans: (libc)Wide Character Case Conversion. * wctype: (libc)Classification of Wide Characters. * wmemchr: (libc)Search Functions. * wmemcmp: (libc)String/Array Comparison. * wmemcpy: (libc)Copying Strings and Arrays. * wmemmove: (libc)Copying Strings and Arrays. * wmempcpy: (libc)Copying Strings and Arrays. * wmemset: (libc)Copying Strings and Arrays. * wordexp: (libc)Calling Wordexp. * wordfree: (libc)Calling Wordexp. * wprintf: (libc)Formatted Output Functions. * write: (libc)I/O Primitives. * writev: (libc)Scatter-Gather. * wscanf: (libc)Formatted Input Functions. * y0: (libc)Special Functions. * y0f: (libc)Special Functions. * y0fN: (libc)Special Functions. * y0fNx: (libc)Special Functions. * y0l: (libc)Special Functions. * y1: (libc)Special Functions. * y1f: (libc)Special Functions. * y1fN: (libc)Special Functions. * y1fNx: (libc)Special Functions. * y1l: (libc)Special Functions. * yn: (libc)Special Functions. * ynf: (libc)Special Functions. * ynfN: (libc)Special Functions. * ynfNx: (libc)Special Functions. * ynl: (libc)Special Functions. END-INFO-DIR-ENTRY  File: libc.info, Node: Printing of Floats, Next: System V Number Conversion, Prev: Parsing of Numbers, Up: Arithmetic 20.12 Printing of Floats ======================== The ‘strfrom’ functions are declared in ‘stdlib.h’. -- Function: int strfromd (char *restrict STRING, size_t SIZE, const char *restrict FORMAT, double VALUE) -- Function: int strfromf (char *restrict STRING, size_t SIZE, const char *restrict FORMAT, float VALUE) -- Function: int strfroml (char *restrict STRING, size_t SIZE, const char *restrict FORMAT, long double VALUE) Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem | *Note POSIX Safety Concepts::. The functions ‘strfromd’ (“string-from-double”), ‘strfromf’ (“string-from-float”), and ‘strfroml’ (“string-from-long-double”) convert the floating-point number VALUE to a string of characters and stores them into the area pointed to by STRING. The conversion writes at most SIZE characters and respects the format specified by FORMAT. The format string must start with the character ‘%’. An optional precision follows, which starts with a period, ‘.’, and may be followed by a decimal integer, representing the precision. If a decimal integer is not specified after the period, the precision is taken to be zero. The character ‘*’ is not allowed. Finally, the format string ends with one of the following conversion specifiers: ‘a’, ‘A’, ‘e’, ‘E’, ‘f’, ‘F’, ‘g’ or ‘G’ (*note Table of Output Conversions::). Invalid format strings result in undefined behavior. These functions return the number of characters that would have been written to STRING had SIZE been sufficiently large, not counting the terminating null character. Thus, the null-terminated output has been completely written if and only if the returned value is less than SIZE. These functions were introduced by ISO/IEC TS 18661-1. -- Function: int strfromfN (char *restrict STRING, size_t SIZE, const char *restrict FORMAT, _FloatN VALUE) -- Function: int strfromfNx (char *restrict STRING, size_t SIZE, const char *restrict FORMAT, _FloatNx VALUE) Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem | *Note POSIX Safety Concepts::. These functions are like ‘strfromd’, except for the type of ‘value’. They were introduced in ISO/IEC TS 18661-3 and are available on machines that support the related types; *note Mathematics::.  File: libc.info, Node: System V Number Conversion, Prev: Printing of Floats, Up: Arithmetic 20.13 Old-fashioned System V number-to-string functions ======================================================= The old System V C library provided three functions to convert numbers to strings, with unusual and hard-to-use semantics. The GNU C Library also provides these functions and some natural extensions. These functions are only available in the GNU C Library and on systems descended from AT&T Unix. Therefore, unless these functions do precisely what you need, it is better to use ‘sprintf’, which is standard. All these functions are defined in ‘stdlib.h’. -- Function: char * ecvt (double VALUE, int NDIGIT, int *DECPT, int *NEG) Preliminary: | MT-Unsafe race:ecvt | AS-Unsafe | AC-Safe | *Note POSIX Safety Concepts::. The function ‘ecvt’ converts the floating-point number VALUE to a string with at most NDIGIT decimal digits. The returned string contains no decimal point or sign. The first digit of the string is non-zero (unless VALUE is actually zero) and the last digit is rounded to nearest. ‘*DECPT’ is set to the index in the string of the first digit after the decimal point. ‘*NEG’ is set to a nonzero value if VALUE is negative, zero otherwise. If NDIGIT decimal digits would exceed the precision of a ‘double’ it is reduced to a system-specific value. The returned string is statically allocated and overwritten by each call to ‘ecvt’. If VALUE is zero, it is implementation defined whether ‘*DECPT’ is ‘0’ or ‘1’. For example: ‘ecvt (12.3, 5, &d, &n)’ returns ‘"12300"’ and sets D to ‘2’ and N to ‘0’. -- Function: char * fcvt (double VALUE, int NDIGIT, int *DECPT, int *NEG) Preliminary: | MT-Unsafe race:fcvt | AS-Unsafe heap | AC-Unsafe mem | *Note POSIX Safety Concepts::. The function ‘fcvt’ is like ‘ecvt’, but NDIGIT specifies the number of digits after the decimal point. If NDIGIT is less than zero, VALUE is rounded to the NDIGIT+1’th place to the left of the decimal point. For example, if NDIGIT is ‘-1’, VALUE will be rounded to the nearest 10. If NDIGIT is negative and larger than the number of digits to the left of the decimal point in VALUE, VALUE will be rounded to one significant digit. If NDIGIT decimal digits would exceed the precision of a ‘double’ it is reduced to a system-specific value. The returned string is statically allocated and overwritten by each call to ‘fcvt’. -- Function: char * gcvt (double VALUE, int NDIGIT, char *BUF) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. ‘gcvt’ is functionally equivalent to ‘sprintf(buf, "%*g", ndigit, value)’. It is provided only for compatibility’s sake. It returns BUF. If NDIGIT decimal digits would exceed the precision of a ‘double’ it is reduced to a system-specific value. As extensions, the GNU C Library provides versions of these three functions that take ‘long double’ arguments. -- Function: char * qecvt (long double VALUE, int NDIGIT, int *DECPT, int *NEG) Preliminary: | MT-Unsafe race:qecvt | AS-Unsafe | AC-Safe | *Note POSIX Safety Concepts::. This function is equivalent to ‘ecvt’ except that it takes a ‘long double’ for the first parameter and that NDIGIT is restricted by the precision of a ‘long double’. -- Function: char * qfcvt (long double VALUE, int NDIGIT, int *DECPT, int *NEG) Preliminary: | MT-Unsafe race:qfcvt | AS-Unsafe heap | AC-Unsafe mem | *Note POSIX Safety Concepts::. This function is equivalent to ‘fcvt’ except that it takes a ‘long double’ for the first parameter and that NDIGIT is restricted by the precision of a ‘long double’. -- Function: char * qgcvt (long double VALUE, int NDIGIT, char *BUF) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is equivalent to ‘gcvt’ except that it takes a ‘long double’ for the first parameter and that NDIGIT is restricted by the precision of a ‘long double’. The ‘ecvt’ and ‘fcvt’ functions, and their ‘long double’ equivalents, all return a string located in a static buffer which is overwritten by the next call to the function. The GNU C Library provides another set of extended functions which write the converted string into a user-supplied buffer. These have the conventional ‘_r’ suffix. ‘gcvt_r’ is not necessary, because ‘gcvt’ already uses a user-supplied buffer. -- Function: int ecvt_r (double VALUE, int NDIGIT, int *DECPT, int *NEG, char *BUF, size_t LEN) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘ecvt_r’ function is the same as ‘ecvt’, except that it places its result into the user-specified buffer pointed to by BUF, with length LEN. The return value is ‘-1’ in case of an error and zero otherwise. This function is a GNU extension. -- Function: int fcvt_r (double VALUE, int NDIGIT, int *DECPT, int *NEG, char *BUF, size_t LEN) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘fcvt_r’ function is the same as ‘fcvt’, except that it places its result into the user-specified buffer pointed to by BUF, with length LEN. The return value is ‘-1’ in case of an error and zero otherwise. This function is a GNU extension. -- Function: int qecvt_r (long double VALUE, int NDIGIT, int *DECPT, int *NEG, char *BUF, size_t LEN) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘qecvt_r’ function is the same as ‘qecvt’, except that it places its result into the user-specified buffer pointed to by BUF, with length LEN. The return value is ‘-1’ in case of an error and zero otherwise. This function is a GNU extension. -- Function: int qfcvt_r (long double VALUE, int NDIGIT, int *DECPT, int *NEG, char *BUF, size_t LEN) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘qfcvt_r’ function is the same as ‘qfcvt’, except that it places its result into the user-specified buffer pointed to by BUF, with length LEN. The return value is ‘-1’ in case of an error and zero otherwise. This function is a GNU extension.  File: libc.info, Node: Date and Time, Next: Resource Usage And Limitation, Prev: Arithmetic, Up: Top 21 Date and Time **************** This chapter describes functions for manipulating dates and times, including functions for determining what time it is and conversion between different time representations. * Menu: * Time Basics:: Concepts and definitions. * Time Types:: Data types to represent time. * Calculating Elapsed Time:: How to calculate the length of an interval. * Processor And CPU Time:: Time a program has spent executing. * Calendar Time:: Manipulation of “real” dates and times. * Setting an Alarm:: Sending a signal after a specified time. * Sleeping:: Waiting for a period of time.  File: libc.info, Node: Time Basics, Next: Time Types, Up: Date and Time 21.1 Time Basics ================ Discussing time in a technical manual can be difficult because the word “time” in English refers to lots of different things. In this manual, we use a rigorous terminology to avoid confusion, and the only thing we use the simple word “time” for is to talk about the abstract concept. A "calendar time" is a point in the time continuum, for example November 4, 1990, at 18:02.5 UTC. Sometimes this is called “absolute time”. We don’t speak of a “date”, because that is inherent in a calendar time. An "interval" is a contiguous part of the time continuum between two calendar times, for example the hour between 9:00 and 10:00 on July 4, 1980. An "elapsed time" is the length of an interval, for example, 35 minutes. People sometimes sloppily use the word “interval” to refer to the elapsed time of some interval. An "amount of time" is a sum of elapsed times, which need not be of any specific intervals. For example, the amount of time it takes to read a book might be 9 hours, independently of when and in how many sittings it is read. A "period" is the elapsed time of an interval between two events, especially when they are part of a sequence of regularly repeating events. A "simple calendar time" is a calendar time represented as an elapsed time since a fixed, implementation-specific calendar time called the "epoch". This representation is convenient for doing calculations on calendar times, such as finding the elapsed time between two calendar times. Simple calendar times are independent of time zone; they represent the same instant in time regardless of where on the globe the computer is. POSIX says that simple calendar times do not include leap seconds, but some (otherwise POSIX-conformant) systems can be configured to include leap seconds in simple calendar times. A "broken-down time" is a calendar time represented by its components in the Gregorian calendar: year, month, day, hour, minute, and second. A broken-down time value is relative to a specific time zone, and so it is also sometimes called a "local time". Broken-down times are most useful for input and output, as they are easier for people to understand, but more difficult to calculate with. "CPU time" measures the amount of time that a single process has actively used a CPU to perform computations. It does not include the time that process has spent waiting for external events. The system tracks the CPU time used by each process separately. "Processor time" measures the amount of time _any_ CPU has been in use by _any_ process. It is a basic system resource, since there’s a limit to how much can exist in any given interval (the elapsed time of the interval times the number of CPUs in the computer) People often call this CPU time, but we reserve the latter term in this manual for the definition above.  File: libc.info, Node: Time Types, Next: Calculating Elapsed Time, Prev: Time Basics, Up: Date and Time 21.2 Time Types =============== ISO C and POSIX define several data types for representing elapsed times, simple calendar times, and broken-down times. -- Data Type: clock_t ‘clock_t’ is used to measure processor and CPU time. It may be an integer or a floating-point type. Its values are counts of "clock ticks" since some arbitrary event in the past. The number of clock ticks per second is system-specific. *Note Processor And CPU Time::, for further detail. -- Data Type: time_t ‘time_t’ is the simplest data type used to represent simple calendar time. In ISO C, ‘time_t’ can be either an integer or a floating-point type, and the meaning of ‘time_t’ values is not specified. The only things a strictly conforming program can do with ‘time_t’ values are: pass them to ‘difftime’ to get the elapsed time between two simple calendar times (*note Calculating Elapsed Time::), and pass them to the functions that convert them to broken-down time (*note Broken-down Time::). On POSIX-conformant systems, ‘time_t’ is an integer type and its values represent the number of seconds elapsed since the "epoch", which is 00:00:00 on January 1, 1970, Coordinated Universal Time. The GNU C Library additionally guarantees that ‘time_t’ is a signed type, and that all of its functions operate correctly on negative ‘time_t’ values, which are interpreted as times before the epoch. -- Data Type: struct timespec ‘struct timespec’ represents a simple calendar time, or an elapsed time, with sub-second resolution. It is declared in ‘time.h’ and has the following members: ‘time_t tv_sec’ The number of whole seconds elapsed since the epoch (for a simple calendar time) or since some other starting point (for an elapsed time). ‘long int tv_nsec’ The number of nanoseconds elapsed since the time given by the ‘tv_sec’ member. When ‘struct timespec’ values are produced by GNU C Library functions, the value in this field will always be greater than or equal to zero, and less than 1,000,000,000. When ‘struct timespec’ values are supplied to GNU C Library functions, the value in this field must be in the same range. -- Data Type: struct timeval ‘struct timeval’ is an older type for representing a simple calendar time, or an elapsed time, with sub-second resolution. It is almost the same as ‘struct timespec’, but provides only microsecond resolution. It is declared in ‘sys/time.h’ and has the following members: ‘time_t tv_sec’ The number of whole seconds elapsed since the epoch (for a simple calendar time) or since some other starting point (for an elapsed time). ‘long int tv_usec’ The number of microseconds elapsed since the time given by the ‘tv_sec’ member. When ‘struct timeval’ values are produced by GNU C Library functions, the value in this field will always be greater than or equal to zero, and less than 1,000,000. When ‘struct timeval’ values are supplied to GNU C Library functions, the value in this field must be in the same range. -- Data Type: struct tm This is the data type used to represent a broken-down time. It has separate fields for year, month, day, and so on. *Note Broken-down Time::, for further details.  File: libc.info, Node: Calculating Elapsed Time, Next: Processor And CPU Time, Prev: Time Types, Up: Date and Time 21.3 Calculating Elapsed Time ============================= Often, one wishes to calculate an elapsed time as the difference between two simple calendar times. The GNU C Library provides only one function for this purpose. -- Function: double difftime (time_t END, time_t BEGIN) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘difftime’ function returns the number of seconds of elapsed time from calendar time BEGIN to calendar time END, as a value of type ‘double’. On POSIX-conformant systems, the advantage of using ‘difftime (END, BEGIN)’ over ‘END - BEGIN’ is that it will produce the mathematically correct result even if END and BEGIN are so far apart that a simple subtraction would overflow. However, if they are so far apart that a ‘double’ cannot exactly represent the difference, the result will be inexact. On other systems, ‘time_t’ values might be encoded in a way that prevents subtraction from working directly, and then ‘difftime’ would be the only way to compute their difference. The GNU C Library does not provide any functions for computing the difference between two values of type ‘struct timeval’ or ‘struct timespec’. Here is the recommended way to do this calculation by hand. It works even on some peculiar operating systems where the ‘tv_sec’ member has an unsigned type. /* Subtract the ‘struct timeval’ values X and Y, storing the result in RESULT. Return 1 if the difference is negative, otherwise 0. */ int timeval_subtract (struct timeval *result, struct timeval *x, struct timeval *y) { /* Perform the carry for the later subtraction by updating Y. */ if (x->tv_usec < y->tv_usec) { int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1; y->tv_usec -= 1000000 * nsec; y->tv_sec += nsec; } if (x->tv_usec - y->tv_usec > 1000000) { int nsec = (x->tv_usec - y->tv_usec) / 1000000; y->tv_usec += 1000000 * nsec; y->tv_sec -= nsec; } /* Compute the time remaining to wait. ‘tv_usec’ is certainly positive. */ result->tv_sec = x->tv_sec - y->tv_sec; result->tv_usec = x->tv_usec - y->tv_usec; /* Return 1 if result is negative. */ return x->tv_sec < y->tv_sec; }  File: libc.info, Node: Processor And CPU Time, Next: Calendar Time, Prev: Calculating Elapsed Time, Up: Date and Time 21.4 Processor And CPU Time =========================== If you’re trying to optimize your program or measure its efficiency, it’s very useful to know how much processor time it uses. For that, calendar time and elapsed times are useless because a process may spend time waiting for I/O or for other processes to use the CPU. However, you can get the information with the functions in this section. CPU time (*note Time Basics::) is represented by the data type ‘clock_t’, which is a number of "clock ticks". It gives the total amount of time a process has actively used a CPU since some arbitrary event. On GNU systems, that event is the creation of the process. While arbitrary in general, the event is always the same event for any particular process, so you can always measure how much time on the CPU a particular computation takes by examining the process’ CPU time before and after the computation. On GNU/Linux and GNU/Hurd systems, ‘clock_t’ is equivalent to ‘long int’ and ‘CLOCKS_PER_SEC’ is an integer value. But in other systems, both ‘clock_t’ and the macro ‘CLOCKS_PER_SEC’ can be either integer or floating-point types. Casting CPU time values to ‘double’, as in the example above, makes sure that operations such as arithmetic and printing work properly and consistently no matter what the underlying representation is. Note that the clock can wrap around. On a 32bit system with ‘CLOCKS_PER_SEC’ set to one million this function will return the same value approximately every 72 minutes. For additional functions to examine a process’ use of processor time, and to control it, see *note Resource Usage And Limitation::. * Menu: * CPU Time:: The ‘clock’ function. * Processor Time:: The ‘times’ function.  File: libc.info, Node: CPU Time, Next: Processor Time, Up: Processor And CPU Time 21.4.1 CPU Time Inquiry ----------------------- To get a process’ CPU time, you can use the ‘clock’ function. This facility is declared in the header file ‘time.h’. In typical usage, you call the ‘clock’ function at the beginning and end of the interval you want to time, subtract the values, and then divide by ‘CLOCKS_PER_SEC’ (the number of clock ticks per second) to get processor time, like this: #include clock_t start, end; double cpu_time_used; start = clock(); … /* Do the work. */ end = clock(); cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC; Do not use a single CPU time as an amount of time; it doesn’t work that way. Either do a subtraction as shown above or query processor time directly. *Note Processor Time::. Different computers and operating systems vary wildly in how they keep track of CPU time. It’s common for the internal processor clock to have a resolution somewhere between a hundredth and millionth of a second. -- Macro: int CLOCKS_PER_SEC The value of this macro is the number of clock ticks per second measured by the ‘clock’ function. POSIX requires that this value be one million independent of the actual resolution. -- Function: clock_t clock (void) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns the calling process’ current CPU time. If the CPU time is not available or cannot be represented, ‘clock’ returns the value ‘(clock_t)(-1)’.  File: libc.info, Node: Processor Time, Prev: CPU Time, Up: Processor And CPU Time 21.4.2 Processor Time Inquiry ----------------------------- The ‘times’ function returns information about a process’ consumption of processor time in a ‘struct tms’ object, in addition to the process’ CPU time. *Note Time Basics::. You should include the header file ‘sys/times.h’ to use this facility. -- Data Type: struct tms The ‘tms’ structure is used to return information about process times. It contains at least the following members: ‘clock_t tms_utime’ This is the total processor time the calling process has used in executing the instructions of its program. ‘clock_t tms_stime’ This is the processor time the system has used on behalf of the calling process. ‘clock_t tms_cutime’ This is the sum of the ‘tms_utime’ values and the ‘tms_cutime’ values of all terminated child processes of the calling process, whose status has been reported to the parent process by ‘wait’ or ‘waitpid’; see *note Process Completion::. In other words, it represents the total processor time used in executing the instructions of all the terminated child processes of the calling process, excluding child processes which have not yet been reported by ‘wait’ or ‘waitpid’. ‘clock_t tms_cstime’ This is similar to ‘tms_cutime’, but represents the total processor time the system has used on behalf of all the terminated child processes of the calling process. All of the times are given in numbers of clock ticks. Unlike CPU time, these are the actual amounts of time; not relative to any event. *Note Creating a Process::. -- Macro: int CLK_TCK This is an obsolete name for the number of clock ticks per second. Use ‘sysconf (_SC_CLK_TCK)’ instead. -- Function: clock_t times (struct tms *BUFFER) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘times’ function stores the processor time information for the calling process in BUFFER. The return value is the number of clock ticks since an arbitrary point in the past, e.g. since system start-up. ‘times’ returns ‘(clock_t)(-1)’ to indicate failure. *Portability Note:* The ‘clock’ function described in *note CPU Time:: is specified by the ISO C standard. The ‘times’ function is a feature of POSIX.1. On GNU systems, the CPU time is defined to be equivalent to the sum of the ‘tms_utime’ and ‘tms_stime’ fields returned by ‘times’.  File: libc.info, Node: Calendar Time, Next: Setting an Alarm, Prev: Processor And CPU Time, Up: Date and Time 21.5 Calendar Time ================== This section describes the functions for getting, setting, and manipulating calendar times. * Menu: * Getting the Time:: Functions for finding out what time it is. * Setting and Adjusting the Time:: Functions for setting and adjusting the system clock. * Broken-down Time:: Facilities for manipulating local time. * Formatting Calendar Time:: Converting times to strings. * Parsing Date and Time:: Convert textual time and date information back into broken-down time values. * TZ Variable:: How users specify the time zone. * Time Zone Functions:: Functions to examine or specify the time zone. * Time Functions Example:: An example program showing use of some of the time functions.  File: libc.info, Node: Getting the Time, Next: Setting and Adjusting the Time, Up: Calendar Time 21.5.1 Getting the Time ----------------------- The GNU C Library provides several functions for getting the current calendar time, with different levels of resolution. -- Function: time_t time (time_t *RESULT) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This is the simplest function for getting the current calendar time. It returns the calendar time as a value of type ‘time_t’; on POSIX systems, that means it has a resolution of one second. It uses the same clock as ‘clock_gettime (CLOCK_REALTIME_COARSE)’, when the clock is available or ‘clock_gettime (CLOCK_REALTIME)’ otherwise. If the argument RESULT is not a null pointer, the calendar time value is also stored in ‘*RESULT’. This function cannot fail. Some applications need more precise timekeeping than is possible with a ‘time_t’ alone. Some applications also need more control over what is meant by “the current time.” For these applications, POSIX provides a function ‘clock_gettime’ that can retrieve the time with up to nanosecond precision, from a variety of different clocks. Clocks can be system-wide, measuring time the same for all processes; or they can be per-process or per-thread, measuring CPU time consumed by a particular process, or some other similar resource. Each clock has its own resolution and epoch. You can find the resolution of a clock with the function ‘clock_getres’. There is no function to get the epoch for a clock; either it is fixed and documented, or the clock is not meant to be used to measure absolute times. -- Data Type: clockid_t The type ‘clockid_t’ is used for constants that indicate which of several system clocks one wishes to use. All systems that support this family of functions will define at least this clock constant: -- Macro: clockid_t CLOCK_REALTIME This clock uses the POSIX epoch, 00:00:00 on January 1, 1970, Coordinated Universal Time. It is close to, but not necessarily in lock-step with, the clocks of ‘time’ (above) and of ‘gettimeofday’ (below). A second clock constant which is not universal, but still very common, is for a clock measuring "monotonic time". Monotonic time is useful for measuring elapsed times, because it guarantees that those measurements are not affected by changes to the system clock. -- Macro: clockid_t CLOCK_MONOTONIC System-wide clock that continuously measures the advancement of calendar time, ignoring discontinuous changes to the system’s setting for absolute calendar time. The epoch for this clock is an unspecified point in the past. The epoch may change if the system is rebooted or suspended. Therefore, ‘CLOCK_MONOTONIC’ cannot be used to measure absolute time, only elapsed time. Systems may support more than just these two clocks. -- Function: int clock_gettime (clockid_t CLOCK, struct timespec *TS) Get the current time accoding to the clock identified by CLOCK, storing it as seconds and nanoseconds in ‘*TS’. *Note Time Types::, for a description of ‘struct timespec’. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error condition is defined for this function: ‘EINVAL’ The clock identified by CLOCK is not supported. ‘clock_gettime’ reports the time scaled to seconds and nanoseconds, but the actual resolution of each clock may not be as fine as one nanosecond, and may not be the same for all clocks. POSIX also provides a function for finding out the actual resolution of a clock: -- Function: int clock_getres (clockid_t CLOCK, struct timespec *RES) Get the actual resolution of the clock identified by CLOCK, storing it in ‘*TS’. For instance, if the clock hardware for ‘CLOCK_REALTIME’ uses a quartz crystal that oscillates at 32.768 kHz, then its resolution would be 30.518 microseconds, and ‘clock_getres (CLOCK_REALTIME, &r)’ would set ‘r.tv_sec’ to 0 and ‘r.tv_nsec’ to 30518. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error condition is defined for this function: ‘EINVAL’ The clock identified by CLOCK is not supported. These functions, and the constants that identify particular clocks, are declared in ‘time.h’. *Portability Note:* On some systems, including systems that use older versions of the GNU C Library, programs that use ‘clock_gettime’ or ‘clock_setres’ must be linked with the ‘-lrt’ library. This has not been necessary with the GNU C Library since version 2.17. The GNU C Library also provides an older, but still widely used, function for getting the current time with a resolution of microseconds. This function is declared in ‘sys/time.h’. -- Function: int gettimeofday (struct timeval *TP, void *TZP) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. Get the current calendar time, storing it as seconds and microseconds in ‘*TP’. *Note Time Types::, for a description of ‘struct timeval’. The clock of ‘gettimeofday’ is close to, but not necessarily in lock-step with, the clocks of ‘time’ and of ‘clock_gettime (CLOCK_REALTIME)’ (see above). On some historic systems, if TZP was not a null pointer, information about a system-wide time zone would be written to ‘*TZP’. This feature is obsolete and not supported on GNU systems. You should always supply a null pointer for this argument. Instead, use the facilities described in *note Time Zone Functions:: and in *note Broken-down Time:: for working with time zones. This function cannot fail, and its return value is always ‘0’. *Portability Note:* As of the 2008 revision of POSIX, this function is considered obsolete. The GNU C Library will continue to provide this function indefinitely, but new programs should use ‘clock_gettime’ instead.  File: libc.info, Node: Setting and Adjusting the Time, Next: Broken-down Time, Prev: Getting the Time, Up: Calendar Time 21.5.2 Setting and Adjusting the Time ------------------------------------- The clock hardware inside a modern computer is quite reliable, but it can still be wrong. The functions in this section allow one to set the system’s idea of the current calendar time, and to adjust the rate at which the system counts seconds, so that the calendar time will both be accurate, and remain accurate. The functions in this section require special privileges to use. *Note Users and Groups::. -- Function: int clock_settime (clockid_t CLOCK, const struct timespec *TS) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. Change the current calendar time, according to the clock identified by CLOCK, to be the simple calendar time in ‘*TS’. Not all of the system’s clocks can be changed. For instance, the ‘CLOCK_REALTIME’ clock can be changed (with the appropriate privileges), but the ‘CLOCK_MONOTONIC’ clock cannot. Because simple calendar times are independent of time zone, this function should not be used when the time zone changes (e.g. if the computer is physically moved from one zone to another). Instead, use the facilities described in *note Time Zone Functions::. ‘clock_settime’ causes the clock to jump forwards or backwards, which can cause a variety of problems. Changing the ‘CLOCK_REALTIME’ clock with ‘clock_settime’ does not affect when timers expire (*note Setting an Alarm::) or when sleeping processes wake up (*note Sleeping::), which avoids some of the problems. Still, for small changes made while the system is running, it is better to use ‘ntp_adjtime’ (below) to make a smooth transition from one time to another. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined for this function: ‘EINVAL’ The clock identified by CLOCK is not supported or cannot be set at all, or the simple calendar time in ‘*TS’ is invalid (for instance, ‘ts->tv_nsec’ is negative or greater than 999,999,999). ‘EPERM’ This process does not have the privileges required to set the clock identified by CLOCK. *Portability Note*: On some systems, including systems that use older versions of the GNU C Library, programs that use ‘clock_settime’ must be linked with the ‘-lrt’ library. This has not been necessary with the GNU C Library since version 2.17. For systems that remain up and running for long periods, it is not enough to set the time once; one should also "discipline" the clock so that it does not drift away from the true calendar time. The ‘ntp_gettime’ and ‘ntp_adjtime’ functions provide an interface to monitor and discipline the system clock. For example, you can fine-tune the rate at which the clock “ticks,” and make small adjustments to the current reported calendar time smoothly, by temporarily speeding up or slowing down the clock. These functions’ names begin with ‘ntp_’ because they were designed for use by programs implementing the Network Time Protocol to synchronize a system’s clock with other systems’ clocks and/or with external high-precision clock hardware. These functions, and the constants and structures they use, are declared in ‘sys/timex.h’. -- Data Type: struct ntptimeval This structure is used to report information about the system clock. It contains the following members: ‘struct timeval time’ The current calendar time, as if retrieved by ‘gettimeofday’. The ‘struct timeval’ data type is described in *note Time Types::. ‘long int maxerror’ This is the maximum error, measured in microseconds. Unless updated via ‘ntp_adjtime’ periodically, this value will reach some platform-specific maximum value. ‘long int esterror’ This is the estimated error, measured in microseconds. This value can be set by ‘ntp_adjtime’ to indicate the estimated offset of the system clock from the true calendar time. -- Function: int ntp_gettime (struct ntptimeval *TPTR) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘ntp_gettime’ function sets the structure pointed to by TPTR to current values. The elements of the structure afterwards contain the values the timer implementation in the kernel assumes. They might or might not be correct. If they are not, an ‘ntp_adjtime’ call is necessary. The return value is ‘0’ on success and other values on failure. The following ‘errno’ error conditions are defined for this function: ‘TIME_ERROR’ The precision clock model is not properly set up at the moment, thus the clock must be considered unsynchronized, and the values should be treated with care. -- Data Type: struct timex This structure is used to control and monitor the system clock. It contains the following members: ‘unsigned int modes’ This variable controls whether and which values are set. Several symbolic constants have to be combined with _binary or_ to specify the effective mode. These constants start with ‘MOD_’. ‘long int offset’ This value indicates the current offset of the system clock from the true calendar time. The value is given in microseconds. If bit ‘MOD_OFFSET’ is set in ‘modes’, the offset (and possibly other dependent values) can be set. The offset’s absolute value must not exceed ‘MAXPHASE’. ‘long int frequency’ This value indicates the difference in frequency between the true calendar time and the system clock. The value is expressed as scaled PPM (parts per million, 0.0001%). The scaling is ‘1 << SHIFT_USEC’. The value can be set with bit ‘MOD_FREQUENCY’, but the absolute value must not exceed ‘MAXFREQ’. ‘long int maxerror’ This is the maximum error, measured in microseconds. A new value can be set using bit ‘MOD_MAXERROR’. Unless updated via ‘ntp_adjtime’ periodically, this value will increase steadily and reach some platform-specific maximum value. ‘long int esterror’ This is the estimated error, measured in microseconds. This value can be set using bit ‘MOD_ESTERROR’. ‘int status’ This variable reflects the various states of the clock machinery. There are symbolic constants for the significant bits, starting with ‘STA_’. Some of these flags can be updated using the ‘MOD_STATUS’ bit. ‘long int constant’ This value represents the bandwidth or stiffness of the PLL (phase locked loop) implemented in the kernel. The value can be changed using bit ‘MOD_TIMECONST’. ‘long int precision’ This value represents the accuracy or the maximum error when reading the system clock. The value is expressed in microseconds. ‘long int tolerance’ This value represents the maximum frequency error of the system clock in scaled PPM. This value is used to increase the ‘maxerror’ every second. ‘struct timeval time’ The current calendar time. ‘long int tick’ The elapsed time between clock ticks in microseconds. A clock tick is a periodic timer interrupt on which the system clock is based. ‘long int ppsfreq’ This is the first of a few optional variables that are present only if the system clock can use a PPS (pulse per second) signal to discipline the system clock. The value is expressed in scaled PPM and it denotes the difference in frequency between the system clock and the PPS signal. ‘long int jitter’ This value expresses a median filtered average of the PPS signal’s dispersion in microseconds. ‘int shift’ This value is a binary exponent for the duration of the PPS calibration interval, ranging from ‘PPS_SHIFT’ to ‘PPS_SHIFTMAX’. ‘long int stabil’ This value represents the median filtered dispersion of the PPS frequency in scaled PPM. ‘long int jitcnt’ This counter represents the number of pulses where the jitter exceeded the allowed maximum ‘MAXTIME’. ‘long int calcnt’ This counter reflects the number of successful calibration intervals. ‘long int errcnt’ This counter represents the number of calibration errors (caused by large offsets or jitter). ‘long int stbcnt’ This counter denotes the number of calibrations where the stability exceeded the threshold. -- Function: int ntp_adjtime (struct timex *TPTR) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘ntp_adjtime’ function sets the structure specified by TPTR to current values. In addition, ‘ntp_adjtime’ updates some settings to match what you pass to it in ‘*TPTR’. Use the ‘modes’ element of ‘*TPTR’ to select what settings to update. You can set ‘offset’, ‘freq’, ‘maxerror’, ‘esterror’, ‘status’, ‘constant’, and ‘tick’. ‘modes’ = zero means set nothing. Only the superuser can update settings. The return value is ‘0’ on success and other values on failure. The following ‘errno’ error conditions are defined for this function: ‘TIME_ERROR’ The high accuracy clock model is not properly set up at the moment, thus the clock must be considered unsynchronized, and the values should be treated with care. Another reason could be that the specified new values are not allowed. ‘EPERM’ The process specified a settings update, but is not superuser. For more details see RFC1305 (Network Time Protocol, Version 3) and related documents. *Portability note:* Early versions of the GNU C Library did not have this function, but did have the synonymous ‘adjtimex’. -- Function: int adjtime (const struct timeval *DELTA, struct timeval *OLDDELTA) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This simpler version of ‘ntp_adjtime’ speeds up or slows down the system clock for a short time, in order to correct it by a small amount. This avoids a discontinuous change in the calendar time reported by the ‘CLOCK_REALTIME’ clock, at the price of having to wait longer for the time to become correct. The DELTA argument specifies a relative adjustment to be made to the clock time. If negative, the system clock is slowed down for a while until it has lost this much elapsed time. If positive, the system clock is speeded up for a while. If the OLDDELTA argument is not a null pointer, the ‘adjtime’ function returns information about any previous time adjustment that has not yet completed. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error condition is defined for this function: ‘EPERM’ This process does not have the privileges required to adjust the ‘CLOCK_REALTIME’ clock. For compatibility, the GNU C Library also provides several older functions for controlling the system time. New programs should prefer to use the functions above. -- Function: int stime (const time_t *NEWTIME) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. Change the ‘CLOCK_REALTIME’ calendar time to be the simple calendar time in ‘*NEWTIME’. Calling this function is exactly the same as calling ‘clock_settime (CLOCK_REALTIME)’, except that the new time can only be set to a precision of one second. This function is no longer available on GNU systems, but it may be the _only_ way to set the time on very old Unix systems, so we continue to document it. If it is available, it is declared in ‘time.h’. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error condition is defined for this function: ‘EPERM’ This process does not have the privileges required to adjust the ‘CLOCK_REALTIME’ clock. -- Function: int adjtimex (struct timex *TIMEX) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. ‘adjtimex’ is an older name for ‘ntp_adjtime’. This function is only available on GNU/Linux systems. It is declared in ‘sys/timex.h’. -- Function: int settimeofday (const struct timeval *TP, const void *TZP) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. Change the ‘CLOCK_REALTIME’ calendar time to be the simple calendar time in ‘*NEWTIME’. This function is declared in ‘sys/time.h’. When TZP is a null pointer, calling this function is exactly the same as calling ‘clock_settime (CLOCK_REALTIME)’, except that the new time can only be set to a precision of one microsecond. When TZP is not a null pointer, the data it points to _may_ be used to set a system-wide idea of the current timezone. This feature is obsolete and not supported on GNU systems. Instead, use the facilities described in *note Time Zone Functions:: and in *note Broken-down Time:: for working with time zones. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined for this function: ‘EPERM’ This process does not have the privileges required to set the ‘CLOCK_REALTIME’ clock. ‘EINVAL’ Neither TP nor TZP is a null pointer. (For historical reasons, it is not possible to set the current time and the current time zone in the same call.) ‘ENOSYS’ The operating system does not support setting time zone information, and TZP is not a null pointer.  File: libc.info, Node: Broken-down Time, Next: Formatting Calendar Time, Prev: Setting and Adjusting the Time, Up: Calendar Time 21.5.3 Broken-down Time ----------------------- Simple calendar times represent absolute times as elapsed times since an epoch. This is convenient for computation, but has no relation to the way people normally think of calendar time. By contrast, "broken-down time" is a binary representation of calendar time separated into year, month, day, and so on. Broken-down time values are not useful for calculations, but they are useful for printing human readable time information. A broken-down time value is always relative to a choice of time zone, and it also indicates which time zone that is. The symbols in this section are declared in the header file ‘time.h’. -- Data Type: struct tm This is the data type used to represent a broken-down time. The structure contains at least the following members, which can appear in any order. ‘int tm_sec’ This is the number of full seconds since the top of the minute (normally in the range ‘0’ through ‘59’, but the actual upper limit is ‘60’, to allow for leap seconds if leap second support is available). ‘int tm_min’ This is the number of full minutes since the top of the hour (in the range ‘0’ through ‘59’). ‘int tm_hour’ This is the number of full hours past midnight (in the range ‘0’ through ‘23’). ‘int tm_mday’ This is the ordinal day of the month (in the range ‘1’ through ‘31’). Watch out for this one! As the only ordinal number in the structure, it is inconsistent with the rest of the structure. ‘int tm_mon’ This is the number of full calendar months since the beginning of the year (in the range ‘0’ through ‘11’). Watch out for this one! People usually use ordinal numbers for month-of-year (where January = 1). ‘int tm_year’ This is the number of full calendar years since 1900. ‘int tm_wday’ This is the number of full days since Sunday (in the range ‘0’ through ‘6’). ‘int tm_yday’ This is the number of full days since the beginning of the year (in the range ‘0’ through ‘365’). ‘int tm_isdst’ This is a flag that indicates whether Daylight Saving Time is (or was, or will be) in effect at the time described. The value is positive if Daylight Saving Time is in effect, zero if it is not, and negative if the information is not available. ‘long int tm_gmtoff’ This field describes the time zone that was used to compute this broken-down time value, including any adjustment for daylight saving; it is the number of seconds that you must add to UTC to get local time. You can also think of this as the number of seconds east of UTC. For example, for U.S. Eastern Standard Time, the value is ‘-5*60*60’. The ‘tm_gmtoff’ field is derived from BSD and is a GNU library extension; it is not visible in a strict ISO C environment. ‘const char *tm_zone’ This field is the name for the time zone that was used to compute this broken-down time value. Like ‘tm_gmtoff’, this field is a BSD and GNU extension, and is not visible in a strict ISO C environment. -- Function: struct tm * localtime (const time_t *TIME) Preliminary: | MT-Unsafe race:tmbuf env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. The ‘localtime’ function converts the simple time pointed to by TIME to broken-down time representation, expressed relative to the user’s specified time zone. The return value is a pointer to a static broken-down time structure, which might be overwritten by subsequent calls to ‘ctime’, ‘gmtime’, or ‘localtime’. (But no other library function overwrites the contents of this object.) The return value is the null pointer if TIME cannot be represented as a broken-down time; typically this is because the year cannot fit into an ‘int’. Calling ‘localtime’ also sets the current time zone as if ‘tzset’ were called. *Note Time Zone Functions::. Using the ‘localtime’ function is a big problem in multi-threaded programs. The result is returned in a static buffer and this is used in all threads. POSIX.1c introduced a variant of this function. -- Function: struct tm * localtime_r (const time_t *TIME, struct tm *RESULTP) Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. The ‘localtime_r’ function works just like the ‘localtime’ function. It takes a pointer to a variable containing a simple time and converts it to the broken-down time format. But the result is not placed in a static buffer. Instead it is placed in the object of type ‘struct tm’ to which the parameter RESULTP points. If the conversion is successful the function returns a pointer to the object the result was written into, i.e., it returns RESULTP. -- Function: struct tm * gmtime (const time_t *TIME) Preliminary: | MT-Unsafe race:tmbuf env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. This function is similar to ‘localtime’, except that the broken-down time is expressed as Coordinated Universal Time (UTC) (formerly called Greenwich Mean Time (GMT)) rather than relative to a local time zone. As for the ‘localtime’ function we have the problem that the result is placed in a static variable. POSIX.1c also provides a replacement for ‘gmtime’. -- Function: struct tm * gmtime_r (const time_t *TIME, struct tm *RESULTP) Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. This function is similar to ‘localtime_r’, except that it converts just like ‘gmtime’ the given time as Coordinated Universal Time. If the conversion is successful the function returns a pointer to the object the result was written into, i.e., it returns RESULTP. -- Function: time_t mktime (struct tm *BROKENTIME) Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. The ‘mktime’ function converts a broken-down time structure to a simple time representation. It also normalizes the contents of the broken-down time structure, and fills in some components based on the values of the others. The ‘mktime’ function ignores the specified contents of the ‘tm_wday’, ‘tm_yday’, ‘tm_gmtoff’, and ‘tm_zone’ members of the broken-down time structure. It uses the values of the other components to determine the calendar time; it’s permissible for these components to have unnormalized values outside their normal ranges. The last thing that ‘mktime’ does is adjust the components of the BROKENTIME structure, including the members that were initially ignored. If the specified broken-down time cannot be represented as a simple time, ‘mktime’ returns a value of ‘(time_t)(-1)’ and does not modify the contents of BROKENTIME. Calling ‘mktime’ also sets the current time zone as if ‘tzset’ were called; ‘mktime’ uses this information instead of BROKENTIME’s initial ‘tm_gmtoff’ and ‘tm_zone’ members. *Note Time Zone Functions::. -- Function: time_t timelocal (struct tm *BROKENTIME) Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. ‘timelocal’ is functionally identical to ‘mktime’, but more mnemonically named. Note that it is the inverse of the ‘localtime’ function. *Portability note:* ‘mktime’ is essentially universally available. ‘timelocal’ is rather rare. -- Function: time_t timegm (struct tm *BROKENTIME) Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. ‘timegm’ is functionally identical to ‘mktime’ except it always takes the input values to be Coordinated Universal Time (UTC) regardless of any local time zone setting. Note that ‘timegm’ is the inverse of ‘gmtime’. *Portability note:* ‘mktime’ is essentially universally available. ‘timegm’ is rather rare. For the most portable conversion from a UTC broken-down time to a simple time, set the ‘TZ’ environment variable to UTC, call ‘mktime’, then set ‘TZ’ back.  File: libc.info, Node: Formatting Calendar Time, Next: Parsing Date and Time, Prev: Broken-down Time, Up: Calendar Time 21.5.4 Formatting Calendar Time ------------------------------- The functions described in this section format calendar time values as strings. These functions are declared in the header file ‘time.h’. -- Function: char * asctime (const struct tm *BROKENTIME) Preliminary: | MT-Unsafe race:asctime locale | AS-Unsafe | AC-Safe | *Note POSIX Safety Concepts::. The ‘asctime’ function converts the broken-down time value that BROKENTIME points to into a string in a standard format: "Tue May 21 13:46:22 1991\n" The abbreviations for the days of week are: ‘Sun’, ‘Mon’, ‘Tue’, ‘Wed’, ‘Thu’, ‘Fri’, and ‘Sat’. The abbreviations for the months are: ‘Jan’, ‘Feb’, ‘Mar’, ‘Apr’, ‘May’, ‘Jun’, ‘Jul’, ‘Aug’, ‘Sep’, ‘Oct’, ‘Nov’, and ‘Dec’. The return value points to a statically allocated string, which might be overwritten by subsequent calls to ‘asctime’ or ‘ctime’. (But no other library function overwrites the contents of this string.) -- Function: char * asctime_r (const struct tm *BROKENTIME, char *BUFFER) Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is similar to ‘asctime’ but instead of placing the result in a static buffer it writes the string in the buffer pointed to by the parameter BUFFER. This buffer should have room for at least 26 bytes, including the terminating null. If no error occurred the function returns a pointer to the string the result was written into, i.e., it returns BUFFER. Otherwise it returns ‘NULL’. -- Function: char * ctime (const time_t *TIME) Preliminary: | MT-Unsafe race:tmbuf race:asctime env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. The ‘ctime’ function is similar to ‘asctime’, except that you specify the calendar time argument as a ‘time_t’ simple time value rather than in broken-down local time format. It is equivalent to asctime (localtime (TIME)) Calling ‘ctime’ also sets the current time zone as if ‘tzset’ were called. *Note Time Zone Functions::. -- Function: char * ctime_r (const time_t *TIME, char *BUFFER) Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. This function is similar to ‘ctime’, but places the result in the string pointed to by BUFFER. It is equivalent to (written using gcc extensions, *note (gcc)Statement Exprs::): ({ struct tm tm; asctime_r (localtime_r (time, &tm), buf); }) If no error occurred the function returns a pointer to the string the result was written into, i.e., it returns BUFFER. Otherwise it returns ‘NULL’. -- Function: size_t strftime (char *S, size_t SIZE, const char *TEMPLATE, const struct tm *BROKENTIME) Preliminary: | MT-Safe env locale | AS-Unsafe corrupt heap lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::. This function is similar to the ‘sprintf’ function (*note Formatted Input::), but the conversion specifications that can appear in the format template TEMPLATE are specialized for printing components of the date and time BROKENTIME according to the locale currently specified for time conversion (*note Locales::) and the current time zone (*note Time Zone Functions::). Ordinary characters appearing in the TEMPLATE are copied to the output string S; this can include multibyte character sequences. Conversion specifiers are introduced by a ‘%’ character, followed by an optional flag which can be one of the following. These flags are all GNU extensions. The first three affect only the output of numbers: ‘_’ The number is padded with spaces. ‘-’ The number is not padded at all. ‘0’ The number is padded with zeros even if the format specifies padding with spaces. ‘^’ The output uses uppercase characters, but only if this is possible (*note Case Conversion::). The default action is to pad the number with zeros to keep it a constant width. Numbers that do not have a range indicated below are never padded, since there is no natural width for them. Following the flag an optional specification of the width is possible. This is specified in decimal notation. If the natural size of the output of the field has less than the specified number of characters, the result is written right adjusted and space padded to the given size. An optional modifier can follow the optional flag and width specification. The modifiers, which were first standardized by POSIX.2-1992 and by ISO C99, are: ‘E’ Use the locale’s alternative representation for date and time. This modifier applies to the ‘%c’, ‘%C’, ‘%x’, ‘%X’, ‘%y’ and ‘%Y’ format specifiers. In a Japanese locale, for example, ‘%Ex’ might yield a date format based on the Japanese Emperors’ reigns. ‘O’ With all format specifiers that produce numbers: use the locale’s alternative numeric symbols. With ‘%B’, ‘%b’, and ‘%h’: use the grammatical form for month names that is appropriate when the month is named by itself, rather than the form that is appropriate when the month is used as part of a complete date. The ‘%OB’ and ‘%Ob’ formats are a C2X feature, specified in C2X to use the locale’s ‘alternative’ month name; the GNU C Library extends this specification to say that the form used in a complete date is the default and the form naming the month by itself is the alternative. If the format supports the modifier but no alternative representation is available, it is ignored. The conversion specifier ends with a format specifier taken from the following list. The whole ‘%’ sequence is replaced in the output string as follows: ‘%a’ The abbreviated weekday name according to the current locale. ‘%A’ The full weekday name according to the current locale. ‘%b’ The abbreviated month name according to the current locale, in the grammatical form used when the month is part of a complete date. As a C2X feature (with a more detailed specification in the GNU C Library), the ‘O’ modifier can be used (‘%Ob’) to get the grammatical form used when the month is named by itself. ‘%B’ The full month name according to the current locale, in the grammatical form used when the month is part of a complete date. As a C2X feature (with a more detailed specification in the GNU C Library), the ‘O’ modifier can be used (‘%OB’) to get the grammatical form used when the month is named by itself. Note that not all languages need two different forms of the month names, so the text produced by ‘%B’ and ‘%OB’, and by ‘%b’ and ‘%Ob’, may or may not be the same, depending on the locale. ‘%c’ The preferred calendar time representation for the current locale. ‘%C’ The century of the year. This is equivalent to the greatest integer not greater than the year divided by 100. If the ‘E’ modifier is specified (‘%EC’), instead produces the name of the period for the year (e.g. an era name) in the locale’s alternative calendar. This format was first standardized by POSIX.2-1992 and by ISO C99. ‘%d’ The day of the month as a decimal number (range ‘01’ through ‘31’). ‘%D’ The date using the format ‘%m/%d/%y’. This format was first standardized by POSIX.2-1992 and by ISO C99. ‘%e’ The day of the month like with ‘%d’, but padded with spaces (range ‘ 1’ through ‘31’). This format was first standardized by POSIX.2-1992 and by ISO C99. ‘%F’ The date using the format ‘%Y-%m-%d’. This is the form specified in the ISO 8601 standard and is the preferred form for all uses. This format was first standardized by ISO C99 and by POSIX.1-2001. ‘%g’ The year corresponding to the ISO week number, but without the century (range ‘00’ through ‘99’). This has the same format and value as ‘%y’, except that if the ISO week number (see ‘%V’) belongs to the previous or next year, that year is used instead. This format was first standardized by ISO C99 and by POSIX.1-2001. ‘%G’ The year corresponding to the ISO week number. This has the same format and value as ‘%Y’, except that if the ISO week number (see ‘%V’) belongs to the previous or next year, that year is used instead. This format was first standardized by ISO C99 and by POSIX.1-2001 but was previously available as a GNU extension. ‘%h’ The abbreviated month name according to the current locale. The action is the same as for ‘%b’. This format was first standardized by POSIX.2-1992 and by ISO C99. ‘%H’ The hour as a decimal number, using a 24-hour clock (range ‘00’ through ‘23’). ‘%I’ The hour as a decimal number, using a 12-hour clock (range ‘01’ through ‘12’). ‘%j’ The day of the year as a decimal number (range ‘001’ through ‘366’). ‘%k’ The hour as a decimal number, using a 24-hour clock like ‘%H’, but padded with spaces (range ‘ 0’ through ‘23’). This format is a GNU extension. ‘%l’ The hour as a decimal number, using a 12-hour clock like ‘%I’, but padded with spaces (range ‘ 1’ through ‘12’). This format is a GNU extension. ‘%m’ The month as a decimal number (range ‘01’ through ‘12’). ‘%M’ The minute as a decimal number (range ‘00’ through ‘59’). ‘%n’ A single ‘\n’ (newline) character. This format was first standardized by POSIX.2-1992 and by ISO C99. ‘%p’ Either ‘AM’ or ‘PM’, according to the given time value; or the corresponding strings for the current locale. Noon is treated as ‘PM’ and midnight as ‘AM’. In most locales ‘AM’/‘PM’ format is not supported, in such cases ‘"%p"’ yields an empty string. ‘%P’ Either ‘am’ or ‘pm’, according to the given time value; or the corresponding strings for the current locale, printed in lowercase characters. Noon is treated as ‘pm’ and midnight as ‘am’. In most locales ‘AM’/‘PM’ format is not supported, in such cases ‘"%P"’ yields an empty string. This format is a GNU extension. ‘%r’ The complete calendar time using the AM/PM format of the current locale. This format was first standardized by POSIX.2-1992 and by ISO C99. In the POSIX locale, this format is equivalent to ‘%I:%M:%S %p’. ‘%R’ The hour and minute in decimal numbers using the format ‘%H:%M’. This format was first standardized by ISO C99 and by POSIX.1-2001 but was previously available as a GNU extension. ‘%s’ The number of seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC. Leap seconds are not counted unless leap second support is available. This format is a GNU extension. ‘%S’ The seconds as a decimal number (range ‘00’ through ‘60’). ‘%t’ A single ‘\t’ (tabulator) character. This format was first standardized by POSIX.2-1992 and by ISO C99. ‘%T’ The time of day using decimal numbers using the format ‘%H:%M:%S’. This format was first standardized by POSIX.2-1992 and by ISO C99. ‘%u’ The day of the week as a decimal number (range ‘1’ through ‘7’), Monday being ‘1’. This format was first standardized by POSIX.2-1992 and by ISO C99. ‘%U’ The week number of the current year as a decimal number (range ‘00’ through ‘53’), starting with the first Sunday as the first day of the first week. Days preceding the first Sunday in the year are considered to be in week ‘00’. ‘%V’ The ISO 8601:1988 week number as a decimal number (range ‘01’ through ‘53’). ISO weeks start with Monday and end with Sunday. Week ‘01’ of a year is the first week which has the majority of its days in that year; this is equivalent to the week containing the year’s first Thursday, and it is also equivalent to the week containing January 4. Week ‘01’ of a year can contain days from the previous year. The week before week ‘01’ of a year is the last week (‘52’ or ‘53’) of the previous year even if it contains days from the new year. This format was first standardized by POSIX.2-1992 and by ISO C99. ‘%w’ The day of the week as a decimal number (range ‘0’ through ‘6’), Sunday being ‘0’. ‘%W’ The week number of the current year as a decimal number (range ‘00’ through ‘53’), starting with the first Monday as the first day of the first week. All days preceding the first Monday in the year are considered to be in week ‘00’. ‘%x’ The preferred date representation for the current locale. ‘%X’ The preferred time of day representation for the current locale. ‘%y’ The year without a century as a decimal number (range ‘00’ through ‘99’). This is equivalent to the year modulo 100. If the ‘E’ modifier is specified (‘%Ey’), instead produces the year number according to a locale-specific alternative calendar. Unlike ‘%y’, the number is _not_ reduced modulo 100. However, by default it is zero-padded to a minimum of two digits (this can be overridden by an explicit field width or by the ‘_’ and ‘-’ flags). ‘%Y’ The year as a decimal number, using the Gregorian calendar. Years before the year ‘1’ are numbered ‘0’, ‘-1’, and so on. If the ‘E’ modifier is specified (‘%EY’), instead produces a complete representation of the year according to the locale’s alternative calendar. Generally this will be some combination of the information produced by ‘%EC’ and ‘%Ey’. As a GNU extension, the formatting flags ‘_’ or ‘-’ may be used with this conversion specifier; they affect how the year number is printed. ‘%z’ RFC 822/ISO 8601:1988 style numeric time zone (e.g., ‘-0600’ or ‘+0100’), or nothing if no time zone is determinable. This format was first standardized by ISO C99 and by POSIX.1-2001 but was previously available as a GNU extension. In the POSIX locale, a full RFC 822 timestamp is generated by the format ‘"%a, %d %b %Y %H:%M:%S %z"’ (or the equivalent ‘"%a, %d %b %Y %T %z"’). ‘%Z’ The time zone abbreviation (empty if the time zone can’t be determined). ‘%%’ A literal ‘%’ character. The SIZE parameter can be used to specify the maximum number of characters to be stored in the array S, including the terminating null character. If the formatted time requires more than SIZE characters, ‘strftime’ returns zero and the contents of the array S are undefined. Otherwise the return value indicates the number of characters placed in the array S, not including the terminating null character. _Warning:_ This convention for the return value which is prescribed in ISO C can lead to problems in some situations. For certain format strings and certain locales the output really can be the empty string and this cannot be discovered by testing the return value only. E.g., in most locales the AM/PM time format is not supported (most of the world uses the 24 hour time representation). In such locales ‘"%p"’ will return the empty string, i.e., the return value is zero. To detect situations like this something similar to the following code should be used: buf[0] = '\1'; len = strftime (buf, bufsize, format, tp); if (len == 0 && buf[0] != '\0') { /* Something went wrong in the strftime call. */ … } If S is a null pointer, ‘strftime’ does not actually write anything, but instead returns the number of characters it would have written. Calling ‘strftime’ also sets the current time zone as if ‘tzset’ were called; ‘strftime’ uses this information instead of BROKENTIME’s ‘tm_gmtoff’ and ‘tm_zone’ members. *Note Time Zone Functions::. For an example of ‘strftime’, see *note Time Functions Example::. -- Function: size_t wcsftime (wchar_t *S, size_t SIZE, const wchar_t *TEMPLATE, const struct tm *BROKENTIME) Preliminary: | MT-Safe env locale | AS-Unsafe corrupt heap lock dlopen | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::. The ‘wcsftime’ function is equivalent to the ‘strftime’ function with the difference that it operates on wide character strings. The buffer where the result is stored, pointed to by S, must be an array of wide characters. The parameter SIZE which specifies the size of the output buffer gives the number of wide characters, not the number of bytes. Also the format string TEMPLATE is a wide character string. Since all characters needed to specify the format string are in the basic character set it is portably possible to write format strings in the C source code using the ‘L"…"’ notation. The parameter BROKENTIME has the same meaning as in the ‘strftime’ call. The ‘wcsftime’ function supports the same flags, modifiers, and format specifiers as the ‘strftime’ function. The return value of ‘wcsftime’ is the number of wide characters stored in ‘s’. When more characters would have to be written than can be placed in the buffer S the return value is zero, with the same problems indicated in the ‘strftime’ documentation.  File: libc.info, Node: Parsing Date and Time, Next: TZ Variable, Prev: Formatting Calendar Time, Up: Calendar Time 21.5.5 Convert textual time and date information back ----------------------------------------------------- The ISO C standard does not specify any functions which can convert the output of the ‘strftime’ function back into a binary format. This led to a variety of more-or-less successful implementations with different interfaces over the years. Then the Unix standard was extended by the addition of two functions: ‘strptime’ and ‘getdate’. Both have strange interfaces but at least they are widely available. * Menu: * Low-Level Time String Parsing:: Interpret string according to given format. * General Time String Parsing:: User-friendly function to parse data and time strings.  File: libc.info, Node: Low-Level Time String Parsing, Next: General Time String Parsing, Up: Parsing Date and Time 21.5.5.1 Interpret string according to given format ................................................... The first function is rather low-level. It is nevertheless frequently used in software since it is better known. Its interface and implementation are heavily influenced by the ‘getdate’ function, which is defined and implemented in terms of calls to ‘strptime’. -- Function: char * strptime (const char *S, const char *FMT, struct tm *TP) Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. The ‘strptime’ function parses the input string S according to the format string FMT and stores its results in the structure TP. The input string could be generated by a ‘strftime’ call or obtained any other way. It does not need to be in a human-recognizable format; e.g. a date passed as ‘"02:1999:9"’ is acceptable, even though it is ambiguous without context. As long as the format string FMT matches the input string the function will succeed. The user has to make sure, though, that the input can be parsed in a unambiguous way. The string ‘"1999112"’ can be parsed using the format ‘"%Y%m%d"’ as 1999-1-12, 1999-11-2, or even 19991-1-2. It is necessary to add appropriate separators to reliably get results. The format string consists of the same components as the format string of the ‘strftime’ function. The only difference is that the flags ‘_’, ‘-’, ‘0’, and ‘^’ are not allowed. Several of the distinct formats of ‘strftime’ do the same work in ‘strptime’ since differences like case of the input do not matter. For reasons of symmetry all formats are supported, though. The modifiers ‘E’ and ‘O’ are also allowed everywhere the ‘strftime’ function allows them. The formats are: ‘%a’ ‘%A’ The weekday name according to the current locale, in abbreviated form or the full name. ‘%b’ ‘%B’ ‘%h’ A month name according to the current locale. All three specifiers will recognize both abbreviated and full month names. If the locale provides two different grammatical forms of month names, all three specifiers will recognize both forms. As a GNU extension, the ‘O’ modifier can be used with these specifiers; it has no effect, as both grammatical forms of month names are recognized. ‘%c’ The date and time representation for the current locale. ‘%Ec’ Like ‘%c’ but the locale’s alternative date and time format is used. ‘%C’ The century of the year. It makes sense to use this format only if the format string also contains the ‘%y’ format. ‘%EC’ The locale’s representation of the period. Unlike ‘%C’ it sometimes makes sense to use this format since some cultures represent years relative to the beginning of eras instead of using the Gregorian years. ‘%d’ ‘%e’ The day of the month as a decimal number (range ‘1’ through ‘31’). Leading zeroes are permitted but not required. ‘%Od’ ‘%Oe’ Same as ‘%d’ but using the locale’s alternative numeric symbols. Leading zeroes are permitted but not required. ‘%D’ Equivalent to ‘%m/%d/%y’. ‘%F’ Equivalent to ‘%Y-%m-%d’, which is the ISO 8601 date format. This is a GNU extension following an ISO C99 extension to ‘strftime’. ‘%g’ The year corresponding to the ISO week number, but without the century (range ‘00’ through ‘99’). _Note:_ Currently, this is not fully implemented. The format is recognized, input is consumed but no field in TM is set. This format is a GNU extension following a GNU extension of ‘strftime’. ‘%G’ The year corresponding to the ISO week number. _Note:_ Currently, this is not fully implemented. The format is recognized, input is consumed but no field in TM is set. This format is a GNU extension following a GNU extension of ‘strftime’. ‘%H’ ‘%k’ The hour as a decimal number, using a 24-hour clock (range ‘00’ through ‘23’). ‘%k’ is a GNU extension following a GNU extension of ‘strftime’. ‘%OH’ Same as ‘%H’ but using the locale’s alternative numeric symbols. ‘%I’ ‘%l’ The hour as a decimal number, using a 12-hour clock (range ‘01’ through ‘12’). ‘%l’ is a GNU extension following a GNU extension of ‘strftime’. ‘%OI’ Same as ‘%I’ but using the locale’s alternative numeric symbols. ‘%j’ The day of the year as a decimal number (range ‘1’ through ‘366’). Leading zeroes are permitted but not required. ‘%m’ The month as a decimal number (range ‘1’ through ‘12’). Leading zeroes are permitted but not required. ‘%Om’ Same as ‘%m’ but using the locale’s alternative numeric symbols. ‘%M’ The minute as a decimal number (range ‘0’ through ‘59’). Leading zeroes are permitted but not required. ‘%OM’ Same as ‘%M’ but using the locale’s alternative numeric symbols. ‘%n’ ‘%t’ Matches any white space. ‘%p’ ‘%P’ The locale-dependent equivalent to ‘AM’ or ‘PM’. This format is not useful unless ‘%I’ or ‘%l’ is also used. Another complication is that the locale might not define these values at all and therefore the conversion fails. ‘%P’ is a GNU extension following a GNU extension to ‘strftime’. ‘%r’ The complete time using the AM/PM format of the current locale. A complication is that the locale might not define this format at all and therefore the conversion fails. ‘%R’ The hour and minute in decimal numbers using the format ‘%H:%M’. ‘%R’ is a GNU extension following a GNU extension to ‘strftime’. ‘%s’ The number of seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC. Leap seconds are not counted unless leap second support is available. ‘%s’ is a GNU extension following a GNU extension to ‘strftime’. ‘%S’ The seconds as a decimal number (range ‘0’ through ‘60’). Leading zeroes are permitted but not required. *NB:* The Unix specification says the upper bound on this value is ‘61’, a result of a decision to allow double leap seconds. You will not see the value ‘61’ because no minute has more than one leap second, but the myth persists. ‘%OS’ Same as ‘%S’ but using the locale’s alternative numeric symbols. ‘%T’ Equivalent to the use of ‘%H:%M:%S’ in this place. ‘%u’ The day of the week as a decimal number (range ‘1’ through ‘7’), Monday being ‘1’. Leading zeroes are permitted but not required. _Note:_ Currently, this is not fully implemented. The format is recognized, input is consumed but no field in TM is set. ‘%U’ The week number of the current year as a decimal number (range ‘0’ through ‘53’). Leading zeroes are permitted but not required. ‘%OU’ Same as ‘%U’ but using the locale’s alternative numeric symbols. ‘%V’ The ISO 8601:1988 week number as a decimal number (range ‘1’ through ‘53’). Leading zeroes are permitted but not required. _Note:_ Currently, this is not fully implemented. The format is recognized, input is consumed but no field in TM is set. ‘%w’ The day of the week as a decimal number (range ‘0’ through ‘6’), Sunday being ‘0’. Leading zeroes are permitted but not required. _Note:_ Currently, this is not fully implemented. The format is recognized, input is consumed but no field in TM is set. ‘%Ow’ Same as ‘%w’ but using the locale’s alternative numeric symbols. ‘%W’ The week number of the current year as a decimal number (range ‘0’ through ‘53’). Leading zeroes are permitted but not required. _Note:_ Currently, this is not fully implemented. The format is recognized, input is consumed but no field in TM is set. ‘%OW’ Same as ‘%W’ but using the locale’s alternative numeric symbols. ‘%x’ The date using the locale’s date format. ‘%Ex’ Like ‘%x’ but the locale’s alternative data representation is used. ‘%X’ The time using the locale’s time format. ‘%EX’ Like ‘%X’ but the locale’s alternative time representation is used. ‘%y’ The year without a century as a decimal number (range ‘0’ through ‘99’). Leading zeroes are permitted but not required. Note that it is questionable to use this format without the ‘%C’ format. The ‘strptime’ function does regard input values in the range 68 to 99 as the years 1969 to 1999 and the values 0 to 68 as the years 2000 to 2068. But maybe this heuristic fails for some input data. Therefore it is best to avoid ‘%y’ completely and use ‘%Y’ instead. ‘%Ey’ The offset from ‘%EC’ in the locale’s alternative representation. ‘%Oy’ The offset of the year (from ‘%C’) using the locale’s alternative numeric symbols. ‘%Y’ The year as a decimal number, using the Gregorian calendar. ‘%EY’ The full alternative year representation. ‘%z’ The offset from GMT in ISO 8601/RFC822 format. ‘%Z’ The timezone name. _Note:_ Currently, this is not fully implemented. The format is recognized, input is consumed but no field in TM is set. ‘%%’ A literal ‘%’ character. All other characters in the format string must have a matching character in the input string. Exceptions are white spaces in the input string which can match zero or more whitespace characters in the format string. *Portability Note:* The XPG standard advises applications to use at least one whitespace character (as specified by ‘isspace’) or other non-alphanumeric characters between any two conversion specifications. The GNU C Library does not have this limitation but other libraries might have trouble parsing formats like ‘"%d%m%Y%H%M%S"’. The ‘strptime’ function processes the input string from right to left. Each of the three possible input elements (white space, literal, or format) are handled one after the other. If the input cannot be matched to the format string the function stops. The remainder of the format and input strings are not processed. The function returns a pointer to the first character it was unable to process. If the input string contains more characters than required by the format string the return value points right after the last consumed input character. If the whole input string is consumed the return value points to the ‘NULL’ byte at the end of the string. If an error occurs, i.e., ‘strptime’ fails to match all of the format string, the function returns ‘NULL’. The specification of the function in the XPG standard is rather vague, leaving out a few important pieces of information. Most importantly, it does not specify what happens to those elements of TM which are not directly initialized by the different formats. The implementations on different Unix systems vary here. The GNU C Library implementation does not touch those fields which are not directly initialized. Exceptions are the ‘tm_wday’ and ‘tm_yday’ elements, which are recomputed if any of the year, month, or date elements changed. This has two implications: • Before calling the ‘strptime’ function for a new input string, you should prepare the TM structure you pass. Normally this will mean initializing all values to zero. Alternatively, you can set all fields to values like ‘INT_MAX’, allowing you to determine which elements were set by the function call. Zero does not work here since it is a valid value for many of the fields. Careful initialization is necessary if you want to find out whether a certain field in TM was initialized by the function call. • You can construct a ‘struct tm’ value with several consecutive ‘strptime’ calls. A useful application of this is e.g. the parsing of two separate strings, one containing date information and the other time information. By parsing one after the other without clearing the structure in-between, you can construct a complete broken-down time. The following example shows a function which parses a string which contains the date information in either US style or ISO 8601 form: const char * parse_date (const char *input, struct tm *tm) { const char *cp; /* First clear the result structure. */ memset (tm, '\0', sizeof (*tm)); /* Try the ISO format first. */ cp = strptime (input, "%F", tm); if (cp == NULL) { /* Does not match. Try the US form. */ cp = strptime (input, "%D", tm); } return cp; }  File: libc.info, Node: General Time String Parsing, Prev: Low-Level Time String Parsing, Up: Parsing Date and Time 21.5.5.2 A More User-friendly Way to Parse Times and Dates .......................................................... The Unix standard defines another function for parsing date strings. The interface is weird, but if the function happens to suit your application it is just fine. It is problematic to use this function in multi-threaded programs or libraries, since it returns a pointer to a static variable, and uses a global variable and global state (an environment variable). -- Variable: getdate_err This variable of type ‘int’ contains the error code of the last unsuccessful call to ‘getdate’. Defined values are: 1 The environment variable ‘DATEMSK’ is not defined or null. 2 The template file denoted by the ‘DATEMSK’ environment variable cannot be opened. 3 Information about the template file cannot retrieved. 4 The template file is not a regular file. 5 An I/O error occurred while reading the template file. 6 Not enough memory available to execute the function. 7 The template file contains no matching template. 8 The input date is invalid, but would match a template otherwise. This includes dates like February 31st, and dates which cannot be represented in a ‘time_t’ variable. -- Function: struct tm * getdate (const char *STRING) Preliminary: | MT-Unsafe race:getdate env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. The interface to ‘getdate’ is the simplest possible for a function to parse a string and return the value. STRING is the input string and the result is returned in a statically-allocated variable. The details about how the string is processed are hidden from the user. In fact, they can be outside the control of the program. Which formats are recognized is controlled by the file named by the environment variable ‘DATEMSK’. This file should contain lines of valid format strings which could be passed to ‘strptime’. The ‘getdate’ function reads these format strings one after the other and tries to match the input string. The first line which completely matches the input string is used. Elements not initialized through the format string retain the values present at the time of the ‘getdate’ function call. The formats recognized by ‘getdate’ are the same as for ‘strptime’. See above for an explanation. There are only a few extensions to the ‘strptime’ behavior: • If the ‘%Z’ format is given the broken-down time is based on the current time of the timezone matched, not of the current timezone of the runtime environment. _Note_: This is not implemented (currently). The problem is that timezone names are not unique. If a fixed timezone is assumed for a given string (say ‘EST’ meaning US East Coast time), then uses for countries other than the USA will fail. So far we have found no good solution to this. • If only the weekday is specified the selected day depends on the current date. If the current weekday is greater than or equal to the ‘tm_wday’ value the current week’s day is chosen, otherwise the day next week is chosen. • A similar heuristic is used when only the month is given and not the year. If the month is greater than or equal to the current month, then the current year is used. Otherwise it wraps to next year. The first day of the month is assumed if one is not explicitly specified. • The current hour, minute, and second are used if the appropriate value is not set through the format. • If no date is given tomorrow’s date is used if the time is smaller than the current time. Otherwise today’s date is taken. It should be noted that the format in the template file need not only contain format elements. The following is a list of possible format strings (taken from the Unix standard): %m %A %B %d, %Y %H:%M:%S %A %B %m/%d/%y %I %p %d,%m,%Y %H:%M at %A the %dst of %B in %Y run job at %I %p,%B %dnd %A den %d. %B %Y %H.%M Uhr As you can see, the template list can contain very specific strings like ‘run job at %I %p,%B %dnd’. Using the above list of templates and assuming the current time is Mon Sep 22 12:19:47 EDT 1986, we can obtain the following results for the given input. Input Match Result Mon %a Mon Sep 22 12:19:47 EDT 1986 Sun %a Sun Sep 28 12:19:47 EDT 1986 Fri %a Fri Sep 26 12:19:47 EDT 1986 September %B Mon Sep 1 12:19:47 EDT 1986 January %B Thu Jan 1 12:19:47 EST 1987 December %B Mon Dec 1 12:19:47 EST 1986 Sep Mon %b %a Mon Sep 1 12:19:47 EDT 1986 Jan Fri %b %a Fri Jan 2 12:19:47 EST 1987 Dec Mon %b %a Mon Dec 1 12:19:47 EST 1986 Jan Wed 1989 %b %a %Y Wed Jan 4 12:19:47 EST 1989 Fri 9 %a %H Fri Sep 26 09:00:00 EDT 1986 Feb 10:30 %b %H:%S Sun Feb 1 10:00:30 EST 1987 10:30 %H:%M Tue Sep 23 10:30:00 EDT 1986 13:30 %H:%M Mon Sep 22 13:30:00 EDT 1986 The return value of the function is a pointer to a static variable of type ‘struct tm’, or a null pointer if an error occurred. The result is only valid until the next ‘getdate’ call, making this function unusable in multi-threaded applications. The ‘errno’ variable is _not_ changed. Error conditions are stored in the global variable ‘getdate_err’. See the description above for a list of the possible error values. _Warning:_ The ‘getdate’ function should _never_ be used in SUID-programs. The reason is obvious: using the ‘DATEMSK’ environment variable you can get the function to open any arbitrary file and chances are high that with some bogus input (such as a binary file) the program will crash. -- Function: int getdate_r (const char *STRING, struct tm *TP) Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. The ‘getdate_r’ function is the reentrant counterpart of ‘getdate’. It does not use the global variable ‘getdate_err’ to signal an error, but instead returns an error code. The same error codes as described in the ‘getdate_err’ documentation above are used, with 0 meaning success. Moreover, ‘getdate_r’ stores the broken-down time in the variable of type ‘struct tm’ pointed to by the second argument, rather than in a static variable. This function is not defined in the Unix standard. Nevertheless it is available on some other Unix systems as well. The warning against using ‘getdate’ in SUID-programs applies to ‘getdate_r’ as well.  File: libc.info, Node: TZ Variable, Next: Time Zone Functions, Prev: Parsing Date and Time, Up: Calendar Time 21.5.6 Specifying the Time Zone with ‘TZ’ ----------------------------------------- In POSIX systems, a user can specify the time zone by means of the ‘TZ’ environment variable. For information about how to set environment variables, see *note Environment Variables::. The functions for accessing the time zone are declared in ‘time.h’. You should not normally need to set ‘TZ’. If the system is configured properly, the default time zone will be correct. You might set ‘TZ’ if you are using a computer over a network from a different time zone, and would like times reported to you in the time zone local to you, rather than what is local to the computer. In POSIX.1 systems the value of the ‘TZ’ variable can be in one of three formats. With the GNU C Library, the most common format is the last one, which can specify a selection from a large database of time zone information for many regions of the world. The first two formats are used to describe the time zone information directly, which is both more cumbersome and less precise. But the POSIX.1 standard only specifies the details of the first two formats, so it is good to be familiar with them in case you come across a POSIX.1 system that doesn’t support a time zone information database. The first format is used when there is no Daylight Saving Time (or summer time) in the local time zone: STD OFFSET The STD string specifies the name of the time zone. It must be three or more characters long and must not contain a leading colon, embedded digits, commas, nor plus and minus signs. There is no space character separating the time zone name from the OFFSET, so these restrictions are necessary to parse the specification correctly. The OFFSET specifies the time value you must add to the local time to get a Coordinated Universal Time value. It has syntax like [‘+’|‘-’]HH[‘:’MM[‘:’SS]]. This is positive if the local time zone is west of the Prime Meridian and negative if it is east. The hour must be between ‘0’ and ‘24’, and the minute and seconds between ‘0’ and ‘59’. For example, here is how we would specify Eastern Standard Time, but without any Daylight Saving Time alternative: EST+5 The second format is used when there is Daylight Saving Time: STD OFFSET DST [OFFSET]‘,’START[‘/’TIME]‘,’END[‘/’TIME] The initial STD and OFFSET specify the standard time zone, as described above. The DST string and OFFSET specify the name and offset for the corresponding Daylight Saving Time zone; if the OFFSET is omitted, it defaults to one hour ahead of standard time. The remainder of the specification describes when Daylight Saving Time is in effect. The START field is when Daylight Saving Time goes into effect and the END field is when the change is made back to standard time. The following formats are recognized for these fields: ‘JN’ This specifies the Julian day, with N between ‘1’ and ‘365’. February 29 is never counted, even in leap years. ‘N’ This specifies the Julian day, with N between ‘0’ and ‘365’. February 29 is counted in leap years. ‘MM.W.D’ This specifies day D of week W of month M. The day D must be between ‘0’ (Sunday) and ‘6’. The week W must be between ‘1’ and ‘5’; week ‘1’ is the first week in which day D occurs, and week ‘5’ specifies the _last_ D day in the month. The month M should be between ‘1’ and ‘12’. The TIME fields specify when, in the local time currently in effect, the change to the other time occurs. If omitted, the default is ‘02:00:00’. The hours part of the time fields can range from −167 through 167; this is an extension to POSIX.1, which allows only the range 0 through 24. Here are some example ‘TZ’ values, including the appropriate Daylight Saving Time and its dates of applicability. In North American Eastern Standard Time (EST) and Eastern Daylight Time (EDT), the normal offset from UTC is 5 hours; since this is west of the prime meridian, the sign is positive. Summer time begins on March’s second Sunday at 2:00am, and ends on November’s first Sunday at 2:00am. EST+5EDT,M3.2.0/2,M11.1.0/2 Israel Standard Time (IST) and Israel Daylight Time (IDT) are 2 hours ahead of the prime meridian in winter, springing forward an hour on March’s fourth Thursday at 26:00 (i.e., 02:00 on the first Friday on or after March 23), and falling back on October’s last Sunday at 02:00. IST-2IDT,M3.4.4/26,M10.5.0 Western Argentina Summer Time (WARST) is 3 hours behind the prime meridian all year. There is a dummy fall-back transition on December 31 at 25:00 daylight saving time (i.e., 24:00 standard time, equivalent to January 1 at 00:00 standard time), and a simultaneous spring-forward transition on January 1 at 00:00 standard time, so daylight saving time is in effect all year and the initial ‘WART’ is a placeholder. WART4WARST,J1/0,J365/25 Western Greenland Time (WGT) and Western Greenland Summer Time (WGST) are 3 hours behind UTC in the winter. Its clocks follow the European Union rules of springing forward by one hour on March’s last Sunday at 01:00 UTC (−02:00 local time) and falling back on October’s last Sunday at 01:00 UTC (−01:00 local time). WGT3WGST,M3.5.0/-2,M10.5.0/-1 The schedule of Daylight Saving Time in any particular jurisdiction has changed over the years. To be strictly correct, the conversion of dates and times in the past should be based on the schedule that was in effect then. However, this format has no facilities to let you specify how the schedule has changed from year to year. The most you can do is specify one particular schedule—usually the present day schedule—and this is used to convert any date, no matter when. For precise time zone specifications, it is best to use the time zone information database (see below). The third format looks like this: :CHARACTERS Each operating system interprets this format differently; in the GNU C Library, CHARACTERS is the name of a file which describes the time zone. If the ‘TZ’ environment variable does not have a value, the operation chooses a time zone by default. In the GNU C Library, the default time zone is like the specification ‘TZ=:/etc/localtime’ (or ‘TZ=:/usr/local/etc/localtime’, depending on how the GNU C Library was configured; *note Installation::). Other C libraries use their own rule for choosing the default time zone, so there is little we can say about them. If CHARACTERS begins with a slash, it is an absolute file name; otherwise the library looks for the file ‘/usr/share/zoneinfo/CHARACTERS’. The ‘zoneinfo’ directory contains data files describing local time zones in many different parts of the world. The names represent major cities, with subdirectories for geographical areas; for example, ‘America/New_York’, ‘Europe/London’, ‘Asia/Hong_Kong’. These data files are installed by the system administrator, who also sets ‘/etc/localtime’ to point to the data file for the local time zone. The files typically come from the Time Zone Database (http://www.iana.org/time-zones) of time zone and daylight saving time information for most regions of the world, which is maintained by a community of volunteers and put in the public domain.  File: libc.info, Node: Time Zone Functions, Next: Time Functions Example, Prev: TZ Variable, Up: Calendar Time 21.5.7 Functions and Variables for Time Zones --------------------------------------------- -- Variable: char * tzname [2] The array ‘tzname’ contains two strings, which are the standard names of the pair of time zones (standard and Daylight Saving) that the user has selected. ‘tzname[0]’ is the name of the standard time zone (for example, ‘"EST"’), and ‘tzname[1]’ is the name for the time zone when Daylight Saving Time is in use (for example, ‘"EDT"’). These correspond to the STD and DST strings (respectively) from the ‘TZ’ environment variable. If Daylight Saving Time is never used, ‘tzname[1]’ is the empty string. The ‘tzname’ array is initialized from the ‘TZ’ environment variable whenever ‘tzset’, ‘ctime’, ‘strftime’, ‘mktime’, or ‘localtime’ is called. If multiple abbreviations have been used (e.g. ‘"EWT"’ and ‘"EDT"’ for U.S. Eastern War Time and Eastern Daylight Time), the array contains the most recent abbreviation. The ‘tzname’ array is required for POSIX.1 compatibility, but in GNU programs it is better to use the ‘tm_zone’ member of the broken-down time structure, since ‘tm_zone’ reports the correct abbreviation even when it is not the latest one. Though the strings are declared as ‘char *’ the user must refrain from modifying these strings. Modifying the strings will almost certainly lead to trouble. -- Function: void tzset (void) Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | *Note POSIX Safety Concepts::. The ‘tzset’ function initializes the ‘tzname’ variable from the value of the ‘TZ’ environment variable. It is not usually necessary for your program to call this function, because it is called automatically when you use the other time conversion functions that depend on the time zone. The following variables are defined for compatibility with System V Unix. Like ‘tzname’, these variables are set by calling ‘tzset’ or the other time conversion functions. -- Variable: long int timezone This contains the difference between UTC and the latest local standard time, in seconds west of UTC. For example, in the U.S. Eastern time zone, the value is ‘5*60*60’. Unlike the ‘tm_gmtoff’ member of the broken-down time structure, this value is not adjusted for daylight saving, and its sign is reversed. In GNU programs it is better to use ‘tm_gmtoff’, since it contains the correct offset even when it is not the latest one. -- Variable: int daylight This variable has a nonzero value if Daylight Saving Time rules apply. A nonzero value does not necessarily mean that Daylight Saving Time is now in effect; it means only that Daylight Saving Time is sometimes in effect.  File: libc.info, Node: Time Functions Example, Prev: Time Zone Functions, Up: Calendar Time 21.5.8 Time Functions Example ----------------------------- Here is an example program showing the use of some of the calendar time functions. #include #include #define SIZE 256 int main (void) { char buffer[SIZE]; time_t curtime; struct tm *loctime; /* Get the current time. */ curtime = time (NULL); /* Convert it to local time representation. */ loctime = localtime (&curtime); /* Print out the date and time in the standard format. */ fputs (asctime (loctime), stdout); /* Print it out in a nice format. */ strftime (buffer, SIZE, "Today is %A, %B %d.\n", loctime); fputs (buffer, stdout); strftime (buffer, SIZE, "The time is %I:%M %p.\n", loctime); fputs (buffer, stdout); return 0; } It produces output like this: Wed Jul 31 13:02:36 1991 Today is Wednesday, July 31. The time is 01:02 PM.  File: libc.info, Node: Setting an Alarm, Next: Sleeping, Prev: Calendar Time, Up: Date and Time 21.6 Setting an Alarm ===================== The ‘alarm’ and ‘setitimer’ functions provide a mechanism for a process to interrupt itself in the future. They do this by setting a timer; when the timer expires, the process receives a signal. Each process has three independent interval timers available: • A real-time timer that counts elapsed time. This timer sends a ‘SIGALRM’ signal to the process when it expires. • A virtual timer that counts processor time used by the process. This timer sends a ‘SIGVTALRM’ signal to the process when it expires. • A profiling timer that counts both processor time used by the process, and processor time spent in system calls on behalf of the process. This timer sends a ‘SIGPROF’ signal to the process when it expires. This timer is useful for profiling in interpreters. The interval timer mechanism does not have the fine granularity necessary for profiling native code. You can only have one timer of each kind set at any given time. If you set a timer that has not yet expired, that timer is simply reset to the new value. You should establish a handler for the appropriate alarm signal using ‘signal’ or ‘sigaction’ before issuing a call to ‘setitimer’ or ‘alarm’. Otherwise, an unusual chain of events could cause the timer to expire before your program establishes the handler. In this case it would be terminated, since termination is the default action for the alarm signals. *Note Signal Handling::. To be able to use the alarm function to interrupt a system call which might block otherwise indefinitely it is important to _not_ set the ‘SA_RESTART’ flag when registering the signal handler using ‘sigaction’. When not using ‘sigaction’ things get even uglier: the ‘signal’ function has fixed semantics with respect to restarts. The BSD semantics for this function is to set the flag. Therefore, if ‘sigaction’ for whatever reason cannot be used, it is necessary to use ‘sysv_signal’ and not ‘signal’. The ‘setitimer’ function is the primary means for setting an alarm. This facility is declared in the header file ‘sys/time.h’. The ‘alarm’ function, declared in ‘unistd.h’, provides a somewhat simpler interface for setting the real-time timer. -- Data Type: struct itimerval This structure is used to specify when a timer should expire. It contains the following members: ‘struct timeval it_interval’ This is the period between successive timer interrupts. If zero, the alarm will only be sent once. ‘struct timeval it_value’ This is the period between now and the first timer interrupt. If zero, the alarm is disabled. The ‘struct timeval’ data type is described in *note Time Types::. -- Function: int setitimer (int WHICH, const struct itimerval *NEW, struct itimerval *OLD) Preliminary: | MT-Safe timer | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘setitimer’ function sets the timer specified by WHICH according to NEW. The WHICH argument can have a value of ‘ITIMER_REAL’, ‘ITIMER_VIRTUAL’, or ‘ITIMER_PROF’. If OLD is not a null pointer, ‘setitimer’ returns information about any previous unexpired timer of the same kind in the structure it points to. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined for this function: ‘EINVAL’ The timer period is too large. -- Function: int getitimer (int WHICH, struct itimerval *OLD) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘getitimer’ function stores information about the timer specified by WHICH in the structure pointed at by OLD. The return value and error conditions are the same as for ‘setitimer’. ‘ITIMER_REAL’ This constant can be used as the WHICH argument to the ‘setitimer’ and ‘getitimer’ functions to specify the real-time timer. ‘ITIMER_VIRTUAL’ This constant can be used as the WHICH argument to the ‘setitimer’ and ‘getitimer’ functions to specify the virtual timer. ‘ITIMER_PROF’ This constant can be used as the WHICH argument to the ‘setitimer’ and ‘getitimer’ functions to specify the profiling timer. -- Function: unsigned int alarm (unsigned int SECONDS) Preliminary: | MT-Safe timer | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘alarm’ function sets the real-time timer to expire in SECONDS seconds. If you want to cancel any existing alarm, you can do this by calling ‘alarm’ with a SECONDS argument of zero. The return value indicates how many seconds remain before the previous alarm would have been sent. If there was no previous alarm, ‘alarm’ returns zero. The ‘alarm’ function could be defined in terms of ‘setitimer’ like this: unsigned int alarm (unsigned int seconds) { struct itimerval old, new; new.it_interval.tv_usec = 0; new.it_interval.tv_sec = 0; new.it_value.tv_usec = 0; new.it_value.tv_sec = (long int) seconds; if (setitimer (ITIMER_REAL, &new, &old) < 0) return 0; else return old.it_value.tv_sec; } There is an example showing the use of the ‘alarm’ function in *note Handler Returns::. If you simply want your process to wait for a given number of seconds, you should use the ‘sleep’ function. *Note Sleeping::. You shouldn’t count on the signal arriving precisely when the timer expires. In a multiprocessing environment there is typically some amount of delay involved. *Portability Note:* The ‘setitimer’ and ‘getitimer’ functions are derived from BSD Unix, while the ‘alarm’ function is specified by the POSIX.1 standard. ‘setitimer’ is more powerful than ‘alarm’, but ‘alarm’ is more widely used.  File: libc.info, Node: Sleeping, Prev: Setting an Alarm, Up: Date and Time 21.7 Sleeping ============= The function ‘sleep’ gives a simple way to make the program wait for a short interval. If your program doesn’t use signals (except to terminate), then you can expect ‘sleep’ to wait reliably throughout the specified interval. Otherwise, ‘sleep’ can return sooner if a signal arrives; if you want to wait for a given interval regardless of signals, use ‘select’ (*note Waiting for I/O::) and don’t specify any descriptors to wait for. -- Function: unsigned int sleep (unsigned int SECONDS) Preliminary: | MT-Unsafe sig:SIGCHLD/linux | AS-Unsafe | AC-Unsafe | *Note POSIX Safety Concepts::. The ‘sleep’ function waits for SECONDS seconds or until a signal is delivered, whichever happens first. If ‘sleep’ returns because the requested interval is over, it returns a value of zero. If it returns because of delivery of a signal, its return value is the remaining time in the sleep interval. The ‘sleep’ function is declared in ‘unistd.h’. Resist the temptation to implement a sleep for a fixed amount of time by using the return value of ‘sleep’, when nonzero, to call ‘sleep’ again. This will work with a certain amount of accuracy as long as signals arrive infrequently. But each signal can cause the eventual wakeup time to be off by an additional second or so. Suppose a few signals happen to arrive in rapid succession by bad luck—there is no limit on how much this could shorten or lengthen the wait. Instead, compute the calendar time at which the program should stop waiting, and keep trying to wait until that calendar time. This won’t be off by more than a second. With just a little more work, you can use ‘select’ and make the waiting period quite accurate. (Of course, heavy system load can cause additional unavoidable delays—unless the machine is dedicated to one application, there is no way you can avoid this.) On some systems, ‘sleep’ can do strange things if your program uses ‘SIGALRM’ explicitly. Even if ‘SIGALRM’ signals are being ignored or blocked when ‘sleep’ is called, ‘sleep’ might return prematurely on delivery of a ‘SIGALRM’ signal. If you have established a handler for ‘SIGALRM’ signals and a ‘SIGALRM’ signal is delivered while the process is sleeping, the action taken might be just to cause ‘sleep’ to return instead of invoking your handler. And, if ‘sleep’ is interrupted by delivery of a signal whose handler requests an alarm or alters the handling of ‘SIGALRM’, this handler and ‘sleep’ will interfere. On GNU systems, it is safe to use ‘sleep’ and ‘SIGALRM’ in the same program, because ‘sleep’ does not work by means of ‘SIGALRM’. -- Function: int nanosleep (const struct timespec *REQUESTED_TIME, struct timespec *REMAINING) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. If resolution to seconds is not enough the ‘nanosleep’ function can be used. As the name suggests the sleep interval can be specified in nanoseconds. The actual elapsed time of the sleep interval might be longer since the system rounds the elapsed time you request up to the next integer multiple of the actual resolution the system can deliver. ‘*REQUESTED_TIME’ is the elapsed time of the interval you want to sleep. The function returns as ‘*REMAINING’ the elapsed time left in the interval for which you requested to sleep. If the interval completed without getting interrupted by a signal, this is zero. ‘struct timespec’ is described in *note Time Types::. If the function returns because the interval is over the return value is zero. If the function returns -1 the global variable ‘errno’ is set to the following values: ‘EINTR’ The call was interrupted because a signal was delivered to the thread. If the REMAINING parameter is not the null pointer the structure pointed to by REMAINING is updated to contain the remaining elapsed time. ‘EINVAL’ The nanosecond value in the REQUESTED_TIME parameter contains an illegal value. Either the value is negative or greater than or equal to 1000 million. This function is a cancellation point in multi-threaded programs. This is a problem if the thread allocates some resources (like memory, file descriptors, semaphores or whatever) at the time ‘nanosleep’ is called. If the thread gets canceled these resources stay allocated until the program ends. To avoid this calls to ‘nanosleep’ should be protected using cancellation handlers. The ‘nanosleep’ function is declared in ‘time.h’.  File: libc.info, Node: Resource Usage And Limitation, Next: Non-Local Exits, Prev: Date and Time, Up: Top 22 Resource Usage And Limitation ******************************** This chapter describes functions for examining how much of various kinds of resources (CPU time, memory, etc.) a process has used and getting and setting limits on future usage. * Menu: * Resource Usage:: Measuring various resources used. * Limits on Resources:: Specifying limits on resource usage. * Priority:: Reading or setting process run priority. * Memory Resources:: Querying memory available resources. * Processor Resources:: Learn about the processors available.  File: libc.info, Node: Resource Usage, Next: Limits on Resources, Up: Resource Usage And Limitation 22.1 Resource Usage =================== The function ‘getrusage’ and the data type ‘struct rusage’ are used to examine the resource usage of a process. They are declared in ‘sys/resource.h’. -- Function: int getrusage (int PROCESSES, struct rusage *RUSAGE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function reports resource usage totals for processes specified by PROCESSES, storing the information in ‘*RUSAGE’. In most systems, PROCESSES has only two valid values: ‘RUSAGE_SELF’ Just the current process. ‘RUSAGE_CHILDREN’ All child processes (direct and indirect) that have already terminated. The return value of ‘getrusage’ is zero for success, and ‘-1’ for failure. ‘EINVAL’ The argument PROCESSES is not valid. One way of getting resource usage for a particular child process is with the function ‘wait4’, which returns totals for a child when it terminates. *Note BSD Wait Functions::. -- Data Type: struct rusage This data type stores various resource usage statistics. It has the following members, and possibly others: ‘struct timeval ru_utime’ Time spent executing user instructions. ‘struct timeval ru_stime’ Time spent in operating system code on behalf of PROCESSES. ‘long int ru_maxrss’ The maximum resident set size used, in kilobytes. That is, the maximum number of kilobytes of physical memory that PROCESSES used simultaneously. ‘long int ru_ixrss’ An integral value expressed in kilobytes times ticks of execution, which indicates the amount of memory used by text that was shared with other processes. ‘long int ru_idrss’ An integral value expressed the same way, which is the amount of unshared memory used for data. ‘long int ru_isrss’ An integral value expressed the same way, which is the amount of unshared memory used for stack space. ‘long int ru_minflt’ The number of page faults which were serviced without requiring any I/O. ‘long int ru_majflt’ The number of page faults which were serviced by doing I/O. ‘long int ru_nswap’ The number of times PROCESSES was swapped entirely out of main memory. ‘long int ru_inblock’ The number of times the file system had to read from the disk on behalf of PROCESSES. ‘long int ru_oublock’ The number of times the file system had to write to the disk on behalf of PROCESSES. ‘long int ru_msgsnd’ Number of IPC messages sent. ‘long int ru_msgrcv’ Number of IPC messages received. ‘long int ru_nsignals’ Number of signals received. ‘long int ru_nvcsw’ The number of times PROCESSES voluntarily invoked a context switch (usually to wait for some service). ‘long int ru_nivcsw’ The number of times an involuntary context switch took place (because a time slice expired, or another process of higher priority was scheduled).  File: libc.info, Node: Limits on Resources, Next: Priority, Prev: Resource Usage, Up: Resource Usage And Limitation 22.2 Limiting Resource Usage ============================ You can specify limits for the resource usage of a process. When the process tries to exceed a limit, it may get a signal, or the system call by which it tried to do so may fail, depending on the resource. Each process initially inherits its limit values from its parent, but it can subsequently change them. There are two per-process limits associated with a resource: "current limit" The current limit is the value the system will not allow usage to exceed. It is also called the “soft limit” because the process being limited can generally raise the current limit at will. "maximum limit" The maximum limit is the maximum value to which a process is allowed to set its current limit. It is also called the “hard limit” because there is no way for a process to get around it. A process may lower its own maximum limit, but only the superuser may increase a maximum limit. The symbols for use with ‘getrlimit’, ‘setrlimit’, ‘getrlimit64’, and ‘setrlimit64’ are defined in ‘sys/resource.h’. -- Function: int getrlimit (int RESOURCE, struct rlimit *RLP) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. Read the current and maximum limits for the resource RESOURCE and store them in ‘*RLP’. The return value is ‘0’ on success and ‘-1’ on failure. The only possible ‘errno’ error condition is ‘EFAULT’. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32-bit system this function is in fact ‘getrlimit64’. Thus, the LFS interface transparently replaces the old interface. -- Function: int getrlimit64 (int RESOURCE, struct rlimit64 *RLP) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is similar to ‘getrlimit’ but its second parameter is a pointer to a variable of type ‘struct rlimit64’, which allows it to read values which wouldn’t fit in the member of a ‘struct rlimit’. If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32-bit machine, this function is available under the name ‘getrlimit’ and so transparently replaces the old interface. -- Function: int setrlimit (int RESOURCE, const struct rlimit *RLP) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. Store the current and maximum limits for the resource RESOURCE in ‘*RLP’. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error condition is possible: ‘EPERM’ • The process tried to raise a current limit beyond the maximum limit. • The process tried to raise a maximum limit, but is not superuser. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32-bit system this function is in fact ‘setrlimit64’. Thus, the LFS interface transparently replaces the old interface. -- Function: int setrlimit64 (int RESOURCE, const struct rlimit64 *RLP) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is similar to ‘setrlimit’ but its second parameter is a pointer to a variable of type ‘struct rlimit64’ which allows it to set values which wouldn’t fit in the member of a ‘struct rlimit’. If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32-bit machine this function is available under the name ‘setrlimit’ and so transparently replaces the old interface. -- Data Type: struct rlimit This structure is used with ‘getrlimit’ to receive limit values, and with ‘setrlimit’ to specify limit values for a particular process and resource. It has two fields: ‘rlim_t rlim_cur’ The current limit ‘rlim_t rlim_max’ The maximum limit. For ‘getrlimit’, the structure is an output; it receives the current values. For ‘setrlimit’, it specifies the new values. For the LFS functions a similar type is defined in ‘sys/resource.h’. -- Data Type: struct rlimit64 This structure is analogous to the ‘rlimit’ structure above, but its components have wider ranges. It has two fields: ‘rlim64_t rlim_cur’ This is analogous to ‘rlimit.rlim_cur’, but with a different type. ‘rlim64_t rlim_max’ This is analogous to ‘rlimit.rlim_max’, but with a different type. Here is a list of resources for which you can specify a limit. Memory and file sizes are measured in bytes. ‘RLIMIT_CPU’ The maximum amount of CPU time the process can use. If it runs for longer than this, it gets a signal: ‘SIGXCPU’. The value is measured in seconds. *Note Operation Error Signals::. ‘RLIMIT_FSIZE’ The maximum size of file the process can create. Trying to write a larger file causes a signal: ‘SIGXFSZ’. *Note Operation Error Signals::. ‘RLIMIT_DATA’ The maximum size of data memory for the process. If the process tries to allocate data memory beyond this amount, the allocation function fails. ‘RLIMIT_STACK’ The maximum stack size for the process. If the process tries to extend its stack past this size, it gets a ‘SIGSEGV’ signal. *Note Program Error Signals::. ‘RLIMIT_CORE’ The maximum size core file that this process can create. If the process terminates and would dump a core file larger than this, then no core file is created. So setting this limit to zero prevents core files from ever being created. ‘RLIMIT_RSS’ The maximum amount of physical memory that this process should get. This parameter is a guide for the system’s scheduler and memory allocator; the system may give the process more memory when there is a surplus. ‘RLIMIT_MEMLOCK’ The maximum amount of memory that can be locked into physical memory (so it will never be paged out). ‘RLIMIT_NPROC’ The maximum number of processes that can be created with the same user ID. If you have reached the limit for your user ID, ‘fork’ will fail with ‘EAGAIN’. *Note Creating a Process::. ‘RLIMIT_NOFILE’ ‘RLIMIT_OFILE’ The maximum number of files that the process can open. If it tries to open more files than this, its open attempt fails with ‘errno’ ‘EMFILE’. *Note Error Codes::. Not all systems support this limit; GNU does, and 4.4 BSD does. ‘RLIMIT_AS’ The maximum size of total memory that this process should get. If the process tries to allocate more memory beyond this amount with, for example, ‘brk’, ‘malloc’, ‘mmap’ or ‘sbrk’, the allocation function fails. ‘RLIM_NLIMITS’ The number of different resource limits. Any valid RESOURCE operand must be less than ‘RLIM_NLIMITS’. -- Constant: rlim_t RLIM_INFINITY This constant stands for a value of “infinity” when supplied as the limit value in ‘setrlimit’. The following are historical functions to do some of what the functions above do. The functions above are better choices. ‘ulimit’ and the command symbols are declared in ‘ulimit.h’. -- Function: long int ulimit (int CMD, …) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. ‘ulimit’ gets the current limit or sets the current and maximum limit for a particular resource for the calling process according to the command CMD. If you are getting a limit, the command argument is the only argument. If you are setting a limit, there is a second argument: ‘long int’ LIMIT which is the value to which you are setting the limit. The CMD values and the operations they specify are: ‘GETFSIZE’ Get the current limit on the size of a file, in units of 512 bytes. ‘SETFSIZE’ Set the current and maximum limit on the size of a file to LIMIT * 512 bytes. There are also some other CMD values that may do things on some systems, but they are not supported. Only the superuser may increase a maximum limit. When you successfully get a limit, the return value of ‘ulimit’ is that limit, which is never negative. When you successfully set a limit, the return value is zero. When the function fails, the return value is ‘-1’ and ‘errno’ is set according to the reason: ‘EPERM’ A process tried to increase a maximum limit, but is not superuser. ‘vlimit’ and its resource symbols are declared in ‘sys/vlimit.h’. -- Function: int vlimit (int RESOURCE, int LIMIT) Preliminary: | MT-Unsafe race:setrlimit | AS-Unsafe | AC-Safe | *Note POSIX Safety Concepts::. ‘vlimit’ sets the current limit for a resource for a process. RESOURCE identifies the resource: ‘LIM_CPU’ Maximum CPU time. Same as ‘RLIMIT_CPU’ for ‘setrlimit’. ‘LIM_FSIZE’ Maximum file size. Same as ‘RLIMIT_FSIZE’ for ‘setrlimit’. ‘LIM_DATA’ Maximum data memory. Same as ‘RLIMIT_DATA’ for ‘setrlimit’. ‘LIM_STACK’ Maximum stack size. Same as ‘RLIMIT_STACK’ for ‘setrlimit’. ‘LIM_CORE’ Maximum core file size. Same as ‘RLIMIT_COR’ for ‘setrlimit’. ‘LIM_MAXRSS’ Maximum physical memory. Same as ‘RLIMIT_RSS’ for ‘setrlimit’. The return value is zero for success, and ‘-1’ with ‘errno’ set accordingly for failure: ‘EPERM’ The process tried to set its current limit beyond its maximum limit.  File: libc.info, Node: Priority, Next: Memory Resources, Prev: Limits on Resources, Up: Resource Usage And Limitation 22.3 Process CPU Priority And Scheduling ======================================== When multiple processes simultaneously require CPU time, the system’s scheduling policy and process CPU priorities determine which processes get it. This section describes how that determination is made and GNU C Library functions to control it. It is common to refer to CPU scheduling simply as scheduling and a process’ CPU priority simply as the process’ priority, with the CPU resource being implied. Bear in mind, though, that CPU time is not the only resource a process uses or that processes contend for. In some cases, it is not even particularly important. Giving a process a high “priority” may have very little effect on how fast a process runs with respect to other processes. The priorities discussed in this section apply only to CPU time. CPU scheduling is a complex issue and different systems do it in wildly different ways. New ideas continually develop and find their way into the intricacies of the various systems’ scheduling algorithms. This section discusses the general concepts, some specifics of systems that commonly use the GNU C Library, and some standards. For simplicity, we talk about CPU contention as if there is only one CPU in the system. But all the same principles apply when a processor has multiple CPUs, and knowing that the number of processes that can run at any one time is equal to the number of CPUs, you can easily extrapolate the information. The functions described in this section are all defined by the POSIX.1 and POSIX.1b standards (the ‘sched…’ functions are POSIX.1b). However, POSIX does not define any semantics for the values that these functions get and set. In this chapter, the semantics are based on the Linux kernel’s implementation of the POSIX standard. As you will see, the Linux implementation is quite the inverse of what the authors of the POSIX syntax had in mind. * Menu: * Absolute Priority:: The first tier of priority. Posix * Realtime Scheduling:: Scheduling among the process nobility * Basic Scheduling Functions:: Get/set scheduling policy, priority * Traditional Scheduling:: Scheduling among the vulgar masses * CPU Affinity:: Limiting execution to certain CPUs  File: libc.info, Node: Absolute Priority, Next: Realtime Scheduling, Up: Priority 22.3.1 Absolute Priority ------------------------ Every process has an absolute priority, and it is represented by a number. The higher the number, the higher the absolute priority. On systems of the past, and most systems today, all processes have absolute priority 0 and this section is irrelevant. In that case, *Note Traditional Scheduling::. Absolute priorities were invented to accommodate realtime systems, in which it is vital that certain processes be able to respond to external events happening in real time, which means they cannot wait around while some other process that _wants to_, but doesn’t _need to_ run occupies the CPU. When two processes are in contention to use the CPU at any instant, the one with the higher absolute priority always gets it. This is true even if the process with the lower priority is already using the CPU (i.e., the scheduling is preemptive). Of course, we’re only talking about processes that are running or “ready to run,” which means they are ready to execute instructions right now. When a process blocks to wait for something like I/O, its absolute priority is irrelevant. *NB:* The term “runnable” is a synonym for “ready to run.” When two processes are running or ready to run and both have the same absolute priority, it’s more interesting. In that case, who gets the CPU is determined by the scheduling policy. If the processes have absolute priority 0, the traditional scheduling policy described in *note Traditional Scheduling:: applies. Otherwise, the policies described in *note Realtime Scheduling:: apply. You normally give an absolute priority above 0 only to a process that can be trusted not to hog the CPU. Such processes are designed to block (or terminate) after relatively short CPU runs. A process begins life with the same absolute priority as its parent process. Functions described in *note Basic Scheduling Functions:: can change it. Only a privileged process can change a process’ absolute priority to something other than ‘0’. Only a privileged process or the target process’ owner can change its absolute priority at all. POSIX requires absolute priority values used with the realtime scheduling policies to be consecutive with a range of at least 32. On Linux, they are 1 through 99. The functions ‘sched_get_priority_max’ and ‘sched_set_priority_min’ portably tell you what the range is on a particular system. 22.3.1.1 Using Absolute Priority ................................ One thing you must keep in mind when designing real time applications is that having higher absolute priority than any other process doesn’t guarantee the process can run continuously. Two things that can wreck a good CPU run are interrupts and page faults. Interrupt handlers live in that limbo between processes. The CPU is executing instructions, but they aren’t part of any process. An interrupt will stop even the highest priority process. So you must allow for slight delays and make sure that no device in the system has an interrupt handler that could cause too long a delay between instructions for your process. Similarly, a page fault causes what looks like a straightforward sequence of instructions to take a long time. The fact that other processes get to run while the page faults in is of no consequence, because as soon as the I/O is complete, the higher priority process will kick them out and run again, but the wait for the I/O itself could be a problem. To neutralize this threat, use ‘mlock’ or ‘mlockall’. There are a few ramifications of the absoluteness of this priority on a single-CPU system that you need to keep in mind when you choose to set a priority and also when you’re working on a program that runs with high absolute priority. Consider a process that has higher absolute priority than any other process in the system and due to a bug in its program, it gets into an infinite loop. It will never cede the CPU. You can’t run a command to kill it because your command would need to get the CPU in order to run. The errant program is in complete control. It controls the vertical, it controls the horizontal. There are two ways to avoid this: 1) keep a shell running somewhere with a higher absolute priority or 2) keep a controlling terminal attached to the high priority process group. All the priority in the world won’t stop an interrupt handler from running and delivering a signal to the process if you hit Control-C. Some systems use absolute priority as a means of allocating a fixed percentage of CPU time to a process. To do this, a super high priority privileged process constantly monitors the process’ CPU usage and raises its absolute priority when the process isn’t getting its entitled share and lowers it when the process is exceeding it. *NB:* The absolute priority is sometimes called the “static priority.” We don’t use that term in this manual because it misses the most important feature of the absolute priority: its absoluteness.  File: libc.info, Node: Realtime Scheduling, Next: Basic Scheduling Functions, Prev: Absolute Priority, Up: Priority 22.3.2 Realtime Scheduling -------------------------- Whenever two processes with the same absolute priority are ready to run, the kernel has a decision to make, because only one can run at a time. If the processes have absolute priority 0, the kernel makes this decision as described in *note Traditional Scheduling::. Otherwise, the decision is as described in this section. If two processes are ready to run but have different absolute priorities, the decision is much simpler, and is described in *note Absolute Priority::. Each process has a scheduling policy. For processes with absolute priority other than zero, there are two available: 1. First Come First Served 2. Round Robin The most sensible case is where all the processes with a certain absolute priority have the same scheduling policy. We’ll discuss that first. In Round Robin, processes share the CPU, each one running for a small quantum of time (“time slice”) and then yielding to another in a circular fashion. Of course, only processes that are ready to run and have the same absolute priority are in this circle. In First Come First Served, the process that has been waiting the longest to run gets the CPU, and it keeps it until it voluntarily relinquishes the CPU, runs out of things to do (blocks), or gets preempted by a higher priority process. First Come First Served, along with maximal absolute priority and careful control of interrupts and page faults, is the one to use when a process absolutely, positively has to run at full CPU speed or not at all. Judicious use of ‘sched_yield’ function invocations by processes with First Come First Served scheduling policy forms a good compromise between Round Robin and First Come First Served. To understand how scheduling works when processes of different scheduling policies occupy the same absolute priority, you have to know the nitty gritty details of how processes enter and exit the ready to run list. In both cases, the ready to run list is organized as a true queue, where a process gets pushed onto the tail when it becomes ready to run and is popped off the head when the scheduler decides to run it. Note that ready to run and running are two mutually exclusive states. When the scheduler runs a process, that process is no longer ready to run and no longer in the ready to run list. When the process stops running, it may go back to being ready to run again. The only difference between a process that is assigned the Round Robin scheduling policy and a process that is assigned First Come First Serve is that in the former case, the process is automatically booted off the CPU after a certain amount of time. When that happens, the process goes back to being ready to run, which means it enters the queue at the tail. The time quantum we’re talking about is small. Really small. This is not your father’s timesharing. For example, with the Linux kernel, the round robin time slice is a thousand times shorter than its typical time slice for traditional scheduling. A process begins life with the same scheduling policy as its parent process. Functions described in *note Basic Scheduling Functions:: can change it. Only a privileged process can set the scheduling policy of a process that has absolute priority higher than 0.  File: libc.info, Node: Basic Scheduling Functions, Next: Traditional Scheduling, Prev: Realtime Scheduling, Up: Priority 22.3.3 Basic Scheduling Functions --------------------------------- This section describes functions in the GNU C Library for setting the absolute priority and scheduling policy of a process. *Portability Note:* On systems that have the functions in this section, the macro _POSIX_PRIORITY_SCHEDULING is defined in ‘’. For the case that the scheduling policy is traditional scheduling, more functions to fine tune the scheduling are in *note Traditional Scheduling::. Don’t try to make too much out of the naming and structure of these functions. They don’t match the concepts described in this manual because the functions are as defined by POSIX.1b, but the implementation on systems that use the GNU C Library is the inverse of what the POSIX structure contemplates. The POSIX scheme assumes that the primary scheduling parameter is the scheduling policy and that the priority value, if any, is a parameter of the scheduling policy. In the implementation, though, the priority value is king and the scheduling policy, if anything, only fine tunes the effect of that priority. The symbols in this section are declared by including file ‘sched.h’. *Portability Note:* In POSIX, the ‘pid_t’ arguments of the functions below refer to process IDs. On Linux, they are actually thread IDs, and control how specific threads are scheduled with regards to the entire system. The resulting behavior does not conform to POSIX. This is why the following description refers to tasks and tasks IDs, and not processes and process IDs. -- Data Type: struct sched_param This structure describes an absolute priority. ‘int sched_priority’ absolute priority value -- Function: int sched_setscheduler (pid_t PID, int POLICY, const struct sched_param *PARAM) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function sets both the absolute priority and the scheduling policy for a task. It assigns the absolute priority value given by PARAM and the scheduling policy POLICY to the task with ID PID, or the calling task if PID is zero. If POLICY is negative, ‘sched_setscheduler’ keeps the existing scheduling policy. The following macros represent the valid values for POLICY: ‘SCHED_OTHER’ Traditional Scheduling ‘SCHED_FIFO’ First In First Out ‘SCHED_RR’ Round Robin On success, the return value is ‘0’. Otherwise, it is ‘-1’ and ‘ERRNO’ is set accordingly. The ‘errno’ values specific to this function are: ‘EPERM’ • The calling task does not have ‘CAP_SYS_NICE’ permission and POLICY is not ‘SCHED_OTHER’ (or it’s negative and the existing policy is not ‘SCHED_OTHER’. • The calling task does not have ‘CAP_SYS_NICE’ permission and its owner is not the target task’s owner. I.e., the effective uid of the calling task is neither the effective nor the real uid of task PID. ‘ESRCH’ There is no task with pid PID and PID is not zero. ‘EINVAL’ • POLICY does not identify an existing scheduling policy. • The absolute priority value identified by *PARAM is outside the valid range for the scheduling policy POLICY (or the existing scheduling policy if POLICY is negative) or PARAM is null. ‘sched_get_priority_max’ and ‘sched_get_priority_min’ tell you what the valid range is. • PID is negative. -- Function: int sched_getscheduler (pid_t PID) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns the scheduling policy assigned to the task with ID PID, or the calling task if PID is zero. The return value is the scheduling policy. See ‘sched_setscheduler’ for the possible values. If the function fails, the return value is instead ‘-1’ and ‘errno’ is set accordingly. The ‘errno’ values specific to this function are: ‘ESRCH’ There is no task with pid PID and it is not zero. ‘EINVAL’ PID is negative. Note that this function is not an exact mate to ‘sched_setscheduler’ because while that function sets the scheduling policy and the absolute priority, this function gets only the scheduling policy. To get the absolute priority, use ‘sched_getparam’. -- Function: int sched_setparam (pid_t PID, const struct sched_param *PARAM) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function sets a task’s absolute priority. It is functionally identical to ‘sched_setscheduler’ with POLICY = ‘-1’. -- Function: int sched_getparam (pid_t PID, struct sched_param *PARAM) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns a task’s absolute priority. PID is the task ID of the task whose absolute priority you want to know. PARAM is a pointer to a structure in which the function stores the absolute priority of the task. On success, the return value is ‘0’. Otherwise, it is ‘-1’ and ‘errno’ is set accordingly. The ‘errno’ values specific to this function are: ‘ESRCH’ There is no task with ID PID and it is not zero. ‘EINVAL’ PID is negative. -- Function: int sched_get_priority_min (int POLICY) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns the lowest absolute priority value that is allowable for a task with scheduling policy POLICY. On Linux, it is 0 for SCHED_OTHER and 1 for everything else. On success, the return value is ‘0’. Otherwise, it is ‘-1’ and ‘ERRNO’ is set accordingly. The ‘errno’ values specific to this function are: ‘EINVAL’ POLICY does not identify an existing scheduling policy. -- Function: int sched_get_priority_max (int POLICY) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns the highest absolute priority value that is allowable for a task that with scheduling policy POLICY. On Linux, it is 0 for SCHED_OTHER and 99 for everything else. On success, the return value is ‘0’. Otherwise, it is ‘-1’ and ‘ERRNO’ is set accordingly. The ‘errno’ values specific to this function are: ‘EINVAL’ POLICY does not identify an existing scheduling policy. -- Function: int sched_rr_get_interval (pid_t PID, struct timespec *INTERVAL) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function returns the length of the quantum (time slice) used with the Round Robin scheduling policy, if it is used, for the task with task ID PID. It returns the length of time as INTERVAL. With a Linux kernel, the round robin time slice is always 150 microseconds, and PID need not even be a real pid. The return value is ‘0’ on success and in the pathological case that it fails, the return value is ‘-1’ and ‘errno’ is set accordingly. There is nothing specific that can go wrong with this function, so there are no specific ‘errno’ values. -- Function: int sched_yield (void) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function voluntarily gives up the task’s claim on the CPU. Technically, ‘sched_yield’ causes the calling task to be made immediately ready to run (as opposed to running, which is what it was before). This means that if it has absolute priority higher than 0, it gets pushed onto the tail of the queue of tasks that share its absolute priority and are ready to run, and it will run again when its turn next arrives. If its absolute priority is 0, it is more complicated, but still has the effect of yielding the CPU to other tasks. If there are no other tasks that share the calling task’s absolute priority, this function doesn’t have any effect. To the extent that the containing program is oblivious to what other processes in the system are doing and how fast it executes, this function appears as a no-op. The return value is ‘0’ on success and in the pathological case that it fails, the return value is ‘-1’ and ‘errno’ is set accordingly. There is nothing specific that can go wrong with this function, so there are no specific ‘errno’ values.  File: libc.info, Node: Traditional Scheduling, Next: CPU Affinity, Prev: Basic Scheduling Functions, Up: Priority 22.3.4 Traditional Scheduling ----------------------------- This section is about the scheduling among processes whose absolute priority is 0. When the system hands out the scraps of CPU time that are left over after the processes with higher absolute priority have taken all they want, the scheduling described herein determines who among the great unwashed processes gets them. * Menu: * Traditional Scheduling Intro:: * Traditional Scheduling Functions::  File: libc.info, Node: Traditional Scheduling Intro, Next: Traditional Scheduling Functions, Up: Traditional Scheduling 22.3.4.1 Introduction To Traditional Scheduling ............................................... Long before there was absolute priority (See *note Absolute Priority::), Unix systems were scheduling the CPU using this system. When POSIX came in like the Romans and imposed absolute priorities to accommodate the needs of realtime processing, it left the indigenous Absolute Priority Zero processes to govern themselves by their own familiar scheduling policy. Indeed, absolute priorities higher than zero are not available on many systems today and are not typically used when they are, being intended mainly for computers that do realtime processing. So this section describes the only scheduling many programmers need to be concerned about. But just to be clear about the scope of this scheduling: Any time a process with an absolute priority of 0 and a process with an absolute priority higher than 0 are ready to run at the same time, the one with absolute priority 0 does not run. If it’s already running when the higher priority ready-to-run process comes into existence, it stops immediately. In addition to its absolute priority of zero, every process has another priority, which we will refer to as "dynamic priority" because it changes over time. The dynamic priority is meaningless for processes with an absolute priority higher than zero. The dynamic priority sometimes determines who gets the next turn on the CPU. Sometimes it determines how long turns last. Sometimes it determines whether a process can kick another off the CPU. In Linux, the value is a combination of these things, but mostly it just determines the length of the time slice. The higher a process’ dynamic priority, the longer a shot it gets on the CPU when it gets one. If it doesn’t use up its time slice before giving up the CPU to do something like wait for I/O, it is favored for getting the CPU back when it’s ready for it, to finish out its time slice. Other than that, selection of processes for new time slices is basically round robin. But the scheduler does throw a bone to the low priority processes: A process’ dynamic priority rises every time it is snubbed in the scheduling process. In Linux, even the fat kid gets to play. The fluctuation of a process’ dynamic priority is regulated by another value: The “nice” value. The nice value is an integer, usually in the range -20 to 20, and represents an upper limit on a process’ dynamic priority. The higher the nice number, the lower that limit. On a typical Linux system, for example, a process with a nice value of 20 can get only 10 milliseconds on the CPU at a time, whereas a process with a nice value of -20 can achieve a high enough priority to get 400 milliseconds. The idea of the nice value is deferential courtesy. In the beginning, in the Unix garden of Eden, all processes shared equally in the bounty of the computer system. But not all processes really need the same share of CPU time, so the nice value gave a courteous process the ability to refuse its equal share of CPU time that others might prosper. Hence, the higher a process’ nice value, the nicer the process is. (Then a snake came along and offered some process a negative nice value and the system became the crass resource allocation system we know today.) Dynamic priorities tend upward and downward with an objective of smoothing out allocation of CPU time and giving quick response time to infrequent requests. But they never exceed their nice limits, so on a heavily loaded CPU, the nice value effectively determines how fast a process runs. In keeping with the socialistic heritage of Unix process priority, a process begins life with the same nice value as its parent process and can raise it at will. A process can also raise the nice value of any other process owned by the same user (or effective user). But only a privileged process can lower its nice value. A privileged process can also raise or lower another process’ nice value. GNU C Library functions for getting and setting nice values are described in *Note Traditional Scheduling Functions::.  File: libc.info, Node: Traditional Scheduling Functions, Prev: Traditional Scheduling Intro, Up: Traditional Scheduling 22.3.4.2 Functions For Traditional Scheduling ............................................. This section describes how you can read and set the nice value of a process. All these symbols are declared in ‘sys/resource.h’. The function and macro names are defined by POSIX, and refer to "priority," but the functions actually have to do with nice values, as the terms are used both in the manual and POSIX. The range of valid nice values depends on the kernel, but typically it runs from ‘-20’ to ‘20’. A lower nice value corresponds to higher priority for the process. These constants describe the range of priority values: ‘PRIO_MIN’ The lowest valid nice value. ‘PRIO_MAX’ The highest valid nice value. -- Function: int getpriority (int CLASS, int ID) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. Return the nice value of a set of processes; CLASS and ID specify which ones (see below). If the processes specified do not all have the same nice value, this returns the lowest value that any of them has. On success, the return value is ‘0’. Otherwise, it is ‘-1’ and ‘errno’ is set accordingly. The ‘errno’ values specific to this function are: ‘ESRCH’ The combination of CLASS and ID does not match any existing process. ‘EINVAL’ The value of CLASS is not valid. If the return value is ‘-1’, it could indicate failure, or it could be the nice value. The only way to make certain is to set ‘errno = 0’ before calling ‘getpriority’, then use ‘errno != 0’ afterward as the criterion for failure. -- Function: int setpriority (int CLASS, int ID, int NICEVAL) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. Set the nice value of a set of processes to NICEVAL; CLASS and ID specify which ones (see below). The return value is ‘0’ on success, and ‘-1’ on failure. The following ‘errno’ error condition are possible for this function: ‘ESRCH’ The combination of CLASS and ID does not match any existing process. ‘EINVAL’ The value of CLASS is not valid. ‘EPERM’ The call would set the nice value of a process which is owned by a different user than the calling process (i.e., the target process’ real or effective uid does not match the calling process’ effective uid) and the calling process does not have ‘CAP_SYS_NICE’ permission. ‘EACCES’ The call would lower the process’ nice value and the process does not have ‘CAP_SYS_NICE’ permission. The arguments CLASS and ID together specify a set of processes in which you are interested. These are the possible values of CLASS: ‘PRIO_PROCESS’ One particular process. The argument ID is a process ID (pid). ‘PRIO_PGRP’ All the processes in a particular process group. The argument ID is a process group ID (pgid). ‘PRIO_USER’ All the processes owned by a particular user (i.e., whose real uid indicates the user). The argument ID is a user ID (uid). If the argument ID is 0, it stands for the calling process, its process group, or its owner (real uid), according to CLASS. -- Function: int nice (int INCREMENT) Preliminary: | MT-Unsafe race:setpriority | AS-Unsafe | AC-Safe | *Note POSIX Safety Concepts::. Increment the nice value of the calling process by INCREMENT. The return value is the new nice value on success, and ‘-1’ on failure. In the case of failure, ‘errno’ will be set to the same values as for ‘setpriority’. Here is an equivalent definition of ‘nice’: int nice (int increment) { int result, old = getpriority (PRIO_PROCESS, 0); result = setpriority (PRIO_PROCESS, 0, old + increment); if (result != -1) return old + increment; else return -1; }  File: libc.info, Node: CPU Affinity, Prev: Traditional Scheduling, Up: Priority 22.3.5 Limiting execution to certain CPUs ----------------------------------------- On a multi-processor system the operating system usually distributes the different processes which are runnable on all available CPUs in a way which allows the system to work most efficiently. Which processes and threads run can be to some extend be control with the scheduling functionality described in the last sections. But which CPU finally executes which process or thread is not covered. There are a number of reasons why a program might want to have control over this aspect of the system as well: • One thread or process is responsible for absolutely critical work which under no circumstances must be interrupted or hindered from making progress by other processes or threads using CPU resources. In this case the special process would be confined to a CPU which no other process or thread is allowed to use. • The access to certain resources (RAM, I/O ports) has different costs from different CPUs. This is the case in NUMA (Non-Uniform Memory Architecture) machines. Preferably memory should be accessed locally but this requirement is usually not visible to the scheduler. Therefore forcing a process or thread to the CPUs which have local access to the most-used memory helps to significantly boost the performance. • In controlled runtimes resource allocation and book-keeping work (for instance garbage collection) is performance local to processors. This can help to reduce locking costs if the resources do not have to be protected from concurrent accesses from different processors. The POSIX standard up to this date is of not much help to solve this problem. The Linux kernel provides a set of interfaces to allow specifying _affinity sets_ for a process. The scheduler will schedule the thread or process on CPUs specified by the affinity masks. The interfaces which the GNU C Library define follow to some extent the Linux kernel interface. -- Data Type: cpu_set_t This data set is a bitset where each bit represents a CPU. How the system’s CPUs are mapped to bits in the bitset is system dependent. The data type has a fixed size; in the unlikely case that the number of bits are not sufficient to describe the CPUs of the system a different interface has to be used. This type is a GNU extension and is defined in ‘sched.h’. To manipulate the bitset, to set and reset bits, a number of macros are defined. Some of the macros take a CPU number as a parameter. Here it is important to never exceed the size of the bitset. The following macro specifies the number of bits in the ‘cpu_set_t’ bitset. -- Macro: int CPU_SETSIZE The value of this macro is the maximum number of CPUs which can be handled with a ‘cpu_set_t’ object. The type ‘cpu_set_t’ should be considered opaque; all manipulation should happen via the next four macros. -- Macro: void CPU_ZERO (cpu_set_t *SET) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro initializes the CPU set SET to be the empty set. This macro is a GNU extension and is defined in ‘sched.h’. -- Macro: void CPU_SET (int CPU, cpu_set_t *SET) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro adds CPU to the CPU set SET. The CPU parameter must not have side effects since it is evaluated more than once. This macro is a GNU extension and is defined in ‘sched.h’. -- Macro: void CPU_CLR (int CPU, cpu_set_t *SET) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro removes CPU from the CPU set SET. The CPU parameter must not have side effects since it is evaluated more than once. This macro is a GNU extension and is defined in ‘sched.h’. -- Macro: int CPU_ISSET (int CPU, const cpu_set_t *SET) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro returns a nonzero value (true) if CPU is a member of the CPU set SET, and zero (false) otherwise. The CPU parameter must not have side effects since it is evaluated more than once. This macro is a GNU extension and is defined in ‘sched.h’. CPU bitsets can be constructed from scratch or the currently installed affinity mask can be retrieved from the system. -- Function: int sched_getaffinity (pid_t PID, size_t CPUSETSIZE, cpu_set_t *CPUSET) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function stores the CPU affinity mask for the process or thread with the ID PID in the CPUSETSIZE bytes long bitmap pointed to by CPUSET. If successful, the function always initializes all bits in the ‘cpu_set_t’ object and returns zero. If PID does not correspond to a process or thread on the system the or the function fails for some other reason, it returns ‘-1’ and ‘errno’ is set to represent the error condition. ‘ESRCH’ No process or thread with the given ID found. ‘EFAULT’ The pointer CPUSET does not point to a valid object. This function is a GNU extension and is declared in ‘sched.h’. Note that it is not portably possible to use this information to retrieve the information for different POSIX threads. A separate interface must be provided for that. -- Function: int sched_setaffinity (pid_t PID, size_t CPUSETSIZE, const cpu_set_t *CPUSET) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function installs the CPUSETSIZE bytes long affinity mask pointed to by CPUSET for the process or thread with the ID PID. If successful the function returns zero and the scheduler will in the future take the affinity information into account. If the function fails it will return ‘-1’ and ‘errno’ is set to the error code: ‘ESRCH’ No process or thread with the given ID found. ‘EFAULT’ The pointer CPUSET does not point to a valid object. ‘EINVAL’ The bitset is not valid. This might mean that the affinity set might not leave a processor for the process or thread to run on. This function is a GNU extension and is declared in ‘sched.h’. -- Function: int getcpu (unsigned int *cpu, unsigned int *node) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘getcpu’ function identifies the processor and node on which the calling thread or process is currently running and writes them into the integers pointed to by the CPU and NODE arguments. The processor is a unique nonnegative integer identifying a CPU. The node is a unique nonnegative integer identifying a NUMA node. When either CPU or NODE is ‘NULL’, nothing is written to the respective pointer. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error condition is defined for this function: ‘ENOSYS’ The operating system does not support this function. This function is Linux-specific and is declared in ‘sched.h’.  File: libc.info, Node: Memory Resources, Next: Processor Resources, Prev: Priority, Up: Resource Usage And Limitation 22.4 Querying memory available resources ======================================== The amount of memory available in the system and the way it is organized determines oftentimes the way programs can and have to work. For functions like ‘mmap’ it is necessary to know about the size of individual memory pages and knowing how much memory is available enables a program to select appropriate sizes for, say, caches. Before we get into these details a few words about memory subsystems in traditional Unix systems will be given. * Menu: * Memory Subsystem:: Overview about traditional Unix memory handling. * Query Memory Parameters:: How to get information about the memory subsystem?  File: libc.info, Node: Memory Subsystem, Next: Query Memory Parameters, Up: Memory Resources 22.4.1 Overview about traditional Unix memory handling ------------------------------------------------------ Unix systems normally provide processes virtual address spaces. This means that the addresses of the memory regions do not have to correspond directly to the addresses of the actual physical memory which stores the data. An extra level of indirection is introduced which translates virtual addresses into physical addresses. This is normally done by the hardware of the processor. Using a virtual address space has several advantages. The most important is process isolation. The different processes running on the system cannot interfere directly with each other. No process can write into the address space of another process (except when shared memory is used but then it is wanted and controlled). Another advantage of virtual memory is that the address space the processes see can actually be larger than the physical memory available. The physical memory can be extended by storage on an external media where the content of currently unused memory regions is stored. The address translation can then intercept accesses to these memory regions and make memory content available again by loading the data back into memory. This concept makes it necessary that programs which have to use lots of memory know the difference between available virtual address space and available physical memory. If the working set of virtual memory of all the processes is larger than the available physical memory the system will slow down dramatically due to constant swapping of memory content from the memory to the storage media and back. This is called “thrashing”. A final aspect of virtual memory which is important and follows from what is said in the last paragraph is the granularity of the virtual address space handling. When we said that the virtual address handling stores memory content externally it cannot do this on a byte-by-byte basis. The administrative overhead does not allow this (leaving alone the processor hardware). Instead several thousand bytes are handled together and form a "page". The size of each page is always a power of two bytes. The smallest page size in use today is 4096, with 8192, 16384, and 65536 being other popular sizes.  File: libc.info, Node: Query Memory Parameters, Prev: Memory Subsystem, Up: Memory Resources 22.4.2 How to get information about the memory subsystem? --------------------------------------------------------- The page size of the virtual memory the process sees is essential to know in several situations. Some programming interfaces (e.g., ‘mmap’, *note Memory-mapped I/O::) require the user to provide information adjusted to the page size. In the case of ‘mmap’ it is necessary to provide a length argument which is a multiple of the page size. Another place where the knowledge about the page size is useful is in memory allocation. If one allocates pieces of memory in larger chunks which are then subdivided by the application code it is useful to adjust the size of the larger blocks to the page size. If the total memory requirement for the block is close (but not larger) to a multiple of the page size the kernel’s memory handling can work more effectively since it only has to allocate memory pages which are fully used. (To do this optimization it is necessary to know a bit about the memory allocator which will require a bit of memory itself for each block and this overhead must not push the total size over the page size multiple.) The page size traditionally was a compile time constant. But recent development of processors changed this. Processors now support different page sizes and they can possibly even vary among different processes on the same system. Therefore the system should be queried at runtime about the current page size and no assumptions (except about it being a power of two) should be made. The correct interface to query about the page size is ‘sysconf’ (*note Sysconf Definition::) with the parameter ‘_SC_PAGESIZE’. There is a much older interface available, too. -- Function: int getpagesize (void) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘getpagesize’ function returns the page size of the process. This value is fixed for the runtime of the process but can vary in different runs of the application. The function is declared in ‘unistd.h’. Widely available on System V derived systems is a method to get information about the physical memory the system has. The call sysconf (_SC_PHYS_PAGES) returns the total number of pages of physical memory the system has. This does not mean all this memory is available. This information can be found using sysconf (_SC_AVPHYS_PAGES) These two values help to optimize applications. The value returned for ‘_SC_AVPHYS_PAGES’ is the amount of memory the application can use without hindering any other process (given that no other process increases its memory usage). The value returned for ‘_SC_PHYS_PAGES’ is more or less a hard limit for the working set. If all applications together constantly use more than that amount of memory the system is in trouble. The GNU C Library provides in addition to these already described way to get this information two functions. They are declared in the file ‘sys/sysinfo.h’. Programmers should prefer to use the ‘sysconf’ method described above. -- Function: long int get_phys_pages (void) Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe lock fd mem | *Note POSIX Safety Concepts::. The ‘get_phys_pages’ function returns the total number of pages of physical memory the system has. To get the amount of memory this number has to be multiplied by the page size. This function is a GNU extension. -- Function: long int get_avphys_pages (void) Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe lock fd mem | *Note POSIX Safety Concepts::. The ‘get_avphys_pages’ function returns the number of available pages of physical memory the system has. To get the amount of memory this number has to be multiplied by the page size. This function is a GNU extension.  File: libc.info, Node: Processor Resources, Prev: Memory Resources, Up: Resource Usage And Limitation 22.5 Learn about the processors available ========================================= The use of threads or processes with shared memory allows an application to take advantage of all the processing power a system can provide. If the task can be parallelized the optimal way to write an application is to have at any time as many processes running as there are processors. To determine the number of processors available to the system one can run sysconf (_SC_NPROCESSORS_CONF) which returns the number of processors the operating system configured. But it might be possible for the operating system to disable individual processors and so the call sysconf (_SC_NPROCESSORS_ONLN) returns the number of processors which are currently online (i.e., available). For these two pieces of information the GNU C Library also provides functions to get the information directly. The functions are declared in ‘sys/sysinfo.h’. -- Function: int get_nprocs_conf (void) Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe lock fd mem | *Note POSIX Safety Concepts::. The ‘get_nprocs_conf’ function returns the number of processors the operating system configured. This function is a GNU extension. -- Function: int get_nprocs (void) Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety Concepts::. The ‘get_nprocs’ function returns the number of available processors. This function is a GNU extension. Before starting more threads it should be checked whether the processors are not already overused. Unix systems calculate something called the "load average". This is a number indicating how many processes were running. This number is an average over different periods of time (normally 1, 5, and 15 minutes). -- Function: int getloadavg (double LOADAVG[], int NELEM) Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety Concepts::. This function gets the 1, 5 and 15 minute load averages of the system. The values are placed in LOADAVG. ‘getloadavg’ will place at most NELEM elements into the array but never more than three elements. The return value is the number of elements written to LOADAVG, or -1 on error. This function is declared in ‘stdlib.h’.  File: libc.info, Node: Non-Local Exits, Next: Signal Handling, Prev: Resource Usage And Limitation, Up: Top 23 Non-Local Exits ****************** Sometimes when your program detects an unusual situation inside a deeply nested set of function calls, you would like to be able to immediately return to an outer level of control. This section describes how you can do such "non-local exits" using the ‘setjmp’ and ‘longjmp’ functions. * Menu: * Intro: Non-Local Intro. When and how to use these facilities. * Details: Non-Local Details. Functions for non-local exits. * Non-Local Exits and Signals:: Portability issues. * System V contexts:: Complete context control a la System V.  File: libc.info, Node: Non-Local Intro, Next: Non-Local Details, Up: Non-Local Exits 23.1 Introduction to Non-Local Exits ==================================== As an example of a situation where a non-local exit can be useful, suppose you have an interactive program that has a “main loop” that prompts for and executes commands. Suppose the “read” command reads input from a file, doing some lexical analysis and parsing of the input while processing it. If a low-level input error is detected, it would be useful to be able to return immediately to the “main loop” instead of having to make each of the lexical analysis, parsing, and processing phases all have to explicitly deal with error situations initially detected by nested calls. (On the other hand, if each of these phases has to do a substantial amount of cleanup when it exits—such as closing files, deallocating buffers or other data structures, and the like—then it can be more appropriate to do a normal return and have each phase do its own cleanup, because a non-local exit would bypass the intervening phases and their associated cleanup code entirely. Alternatively, you could use a non-local exit but do the cleanup explicitly either before or after returning to the “main loop”.) In some ways, a non-local exit is similar to using the ‘return’ statement to return from a function. But while ‘return’ abandons only a single function call, transferring control back to the point at which it was called, a non-local exit can potentially abandon many levels of nested function calls. You identify return points for non-local exits by calling the function ‘setjmp’. This function saves information about the execution environment in which the call to ‘setjmp’ appears in an object of type ‘jmp_buf’. Execution of the program continues normally after the call to ‘setjmp’, but if an exit is later made to this return point by calling ‘longjmp’ with the corresponding ‘jmp_buf’ object, control is transferred back to the point where ‘setjmp’ was called. The return value from ‘setjmp’ is used to distinguish between an ordinary return and a return made by a call to ‘longjmp’, so calls to ‘setjmp’ usually appear in an ‘if’ statement. Here is how the example program described above might be set up: #include #include #include jmp_buf main_loop; void abort_to_main_loop (int status) { longjmp (main_loop, status); } int main (void) { while (1) if (setjmp (main_loop)) puts ("Back at main loop...."); else do_command (); } void do_command (void) { char buffer[128]; if (fgets (buffer, 128, stdin) == NULL) abort_to_main_loop (-1); else exit (EXIT_SUCCESS); } The function ‘abort_to_main_loop’ causes an immediate transfer of control back to the main loop of the program, no matter where it is called from. The flow of control inside the ‘main’ function may appear a little mysterious at first, but it is actually a common idiom with ‘setjmp’. A normal call to ‘setjmp’ returns zero, so the “else” clause of the conditional is executed. If ‘abort_to_main_loop’ is called somewhere within the execution of ‘do_command’, then it actually appears as if the _same_ call to ‘setjmp’ in ‘main’ were returning a second time with a value of ‘-1’. So, the general pattern for using ‘setjmp’ looks something like: if (setjmp (BUFFER)) /* Code to clean up after premature return. */ … else /* Code to be executed normally after setting up the return point. */ …  File: libc.info, Node: Non-Local Details, Next: Non-Local Exits and Signals, Prev: Non-Local Intro, Up: Non-Local Exits 23.2 Details of Non-Local Exits =============================== Here are the details on the functions and data structures used for performing non-local exits. These facilities are declared in ‘setjmp.h’. -- Data Type: jmp_buf Objects of type ‘jmp_buf’ hold the state information to be restored by a non-local exit. The contents of a ‘jmp_buf’ identify a specific place to return to. -- Macro: int setjmp (jmp_buf STATE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. When called normally, ‘setjmp’ stores information about the execution state of the program in STATE and returns zero. If ‘longjmp’ is later used to perform a non-local exit to this STATE, ‘setjmp’ returns a nonzero value. -- Function: void longjmp (jmp_buf STATE, int VALUE) Preliminary: | MT-Safe | AS-Unsafe plugin corrupt lock/hurd | AC-Unsafe corrupt lock/hurd | *Note POSIX Safety Concepts::. This function restores current execution to the state saved in STATE, and continues execution from the call to ‘setjmp’ that established that return point. Returning from ‘setjmp’ by means of ‘longjmp’ returns the VALUE argument that was passed to ‘longjmp’, rather than ‘0’. (But if VALUE is given as ‘0’, ‘setjmp’ returns ‘1’). There are a lot of obscure but important restrictions on the use of ‘setjmp’ and ‘longjmp’. Most of these restrictions are present because non-local exits require a fair amount of magic on the part of the C compiler and can interact with other parts of the language in strange ways. The ‘setjmp’ function is actually a macro without an actual function definition, so you shouldn’t try to ‘#undef’ it or take its address. In addition, calls to ‘setjmp’ are safe in only the following contexts: • As the test expression of a selection or iteration statement (such as ‘if’, ‘switch’, or ‘while’). • As one operand of an equality or comparison operator that appears as the test expression of a selection or iteration statement. The other operand must be an integer constant expression. • As the operand of a unary ‘!’ operator, that appears as the test expression of a selection or iteration statement. • By itself as an expression statement. Return points are valid only during the dynamic extent of the function that called ‘setjmp’ to establish them. If you ‘longjmp’ to a return point that was established in a function that has already returned, unpredictable and disastrous things are likely to happen. You should use a nonzero VALUE argument to ‘longjmp’. While ‘longjmp’ refuses to pass back a zero argument as the return value from ‘setjmp’, this is intended as a safety net against accidental misuse and is not really good programming style. When you perform a non-local exit, accessible objects generally retain whatever values they had at the time ‘longjmp’ was called. The exception is that the values of automatic variables local to the function containing the ‘setjmp’ call that have been changed since the call to ‘setjmp’ are indeterminate, unless you have declared them ‘volatile’.  File: libc.info, Node: Non-Local Exits and Signals, Next: System V contexts, Prev: Non-Local Details, Up: Non-Local Exits 23.3 Non-Local Exits and Signals ================================ In BSD Unix systems, ‘setjmp’ and ‘longjmp’ also save and restore the set of blocked signals; see *note Blocking Signals::. However, the POSIX.1 standard requires ‘setjmp’ and ‘longjmp’ not to change the set of blocked signals, and provides an additional pair of functions (‘sigsetjmp’ and ‘siglongjmp’) to get the BSD behavior. The behavior of ‘setjmp’ and ‘longjmp’ in the GNU C Library is controlled by feature test macros; see *note Feature Test Macros::. The default in the GNU C Library is the POSIX.1 behavior rather than the BSD behavior. The facilities in this section are declared in the header file ‘setjmp.h’. -- Data Type: sigjmp_buf This is similar to ‘jmp_buf’, except that it can also store state information about the set of blocked signals. -- Function: int sigsetjmp (sigjmp_buf STATE, int SAVESIGS) Preliminary: | MT-Safe | AS-Unsafe lock/hurd | AC-Unsafe lock/hurd | *Note POSIX Safety Concepts::. This is similar to ‘setjmp’. If SAVESIGS is nonzero, the set of blocked signals is saved in STATE and will be restored if a ‘siglongjmp’ is later performed with this STATE. -- Function: void siglongjmp (sigjmp_buf STATE, int VALUE) Preliminary: | MT-Safe | AS-Unsafe plugin corrupt lock/hurd | AC-Unsafe corrupt lock/hurd | *Note POSIX Safety Concepts::. This is similar to ‘longjmp’ except for the type of its STATE argument. If the ‘sigsetjmp’ call that set this STATE used a nonzero SAVESIGS flag, ‘siglongjmp’ also restores the set of blocked signals.  File: libc.info, Node: System V contexts, Prev: Non-Local Exits and Signals, Up: Non-Local Exits 23.4 Complete Context Control ============================= The Unix standard provides one more set of functions to control the execution path and these functions are more powerful than those discussed in this chapter so far. These functions were part of the original System V API and by this route were added to the Unix API. Besides on branded Unix implementations these interfaces are not widely available. Not all platforms and/or architectures the GNU C Library is available on provide this interface. Use ‘configure’ to detect the availability. Similar to the ‘jmp_buf’ and ‘sigjmp_buf’ types used for the variables to contain the state of the ‘longjmp’ functions the interfaces of interest here have an appropriate type as well. Objects of this type are normally much larger since more information is contained. The type is also used in a few more places as we will see. The types and functions described in this section are all defined and declared respectively in the ‘ucontext.h’ header file. -- Data Type: ucontext_t The ‘ucontext_t’ type is defined as a structure with at least the following elements: ‘ucontext_t *uc_link’ This is a pointer to the next context structure which is used if the context described in the current structure returns. ‘sigset_t uc_sigmask’ Set of signals which are blocked when this context is used. ‘stack_t uc_stack’ Stack used for this context. The value need not be (and normally is not) the stack pointer. *Note Signal Stack::. ‘mcontext_t uc_mcontext’ This element contains the actual state of the process. The ‘mcontext_t’ type is also defined in this header but the definition should be treated as opaque. Any use of knowledge of the type makes applications less portable. Objects of this type have to be created by the user. The initialization and modification happens through one of the following functions: -- Function: int getcontext (ucontext_t *UCP) Preliminary: | MT-Safe race:ucp | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘getcontext’ function initializes the variable pointed to by UCP with the context of the calling thread. The context contains the content of the registers, the signal mask, and the current stack. Executing the contents would start at the point where the ‘getcontext’ call just returned. *Compatibility Note:* Depending on the operating system, information about the current context’s stack may be in the ‘uc_stack’ field of UCP, or it may instead be in architecture-specific subfields of the ‘uc_mcontext’ field. The function returns ‘0’ if successful. Otherwise it returns ‘-1’ and sets ‘errno’ accordingly. The ‘getcontext’ function is similar to ‘setjmp’ but it does not provide an indication of whether ‘getcontext’ is returning for the first time or whether an initialized context has just been restored. If this is necessary the user has to determine this herself. This must be done carefully since the context contains registers which might contain register variables. This is a good situation to define variables with ‘volatile’. Once the context variable is initialized it can be used as is or it can be modified using the ‘makecontext’ function. The latter is normally done when implementing co-routines or similar constructs. -- Function: void makecontext (ucontext_t *UCP, void (*FUNC) (void), int ARGC, …) Preliminary: | MT-Safe race:ucp | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The UCP parameter passed to ‘makecontext’ shall be initialized by a call to ‘getcontext’. The context will be modified in a way such that if the context is resumed it will start by calling the function ‘func’ which gets ARGC integer arguments passed. The integer arguments which are to be passed should follow the ARGC parameter in the call to ‘makecontext’. Before the call to this function the ‘uc_stack’ and ‘uc_link’ element of the UCP structure should be initialized. The ‘uc_stack’ element describes the stack which is used for this context. No two contexts which are used at the same time should use the same memory region for a stack. The ‘uc_link’ element of the object pointed to by UCP should be a pointer to the context to be executed when the function FUNC returns or it should be a null pointer. See ‘setcontext’ for more information about the exact use. While allocating the memory for the stack one has to be careful. Most modern processors keep track of whether a certain memory region is allowed to contain code which is executed or not. Data segments and heap memory are normally not tagged to allow this. The result is that programs would fail. Examples for such code include the calling sequences the GNU C compiler generates for calls to nested functions. Safe ways to allocate stacks correctly include using memory on the original thread’s stack or explicitly allocating memory tagged for execution using (*note Memory-mapped I/O::). *Compatibility note*: The current Unix standard is very imprecise about the way the stack is allocated. All implementations seem to agree that the ‘uc_stack’ element must be used but the values stored in the elements of the ‘stack_t’ value are unclear. The GNU C Library and most other Unix implementations require the ‘ss_sp’ value of the ‘uc_stack’ element to point to the base of the memory region allocated for the stack and the size of the memory region is stored in ‘ss_size’. There are implementations out there which require ‘ss_sp’ to be set to the value the stack pointer will have (which can, depending on the direction the stack grows, be different). This difference makes the ‘makecontext’ function hard to use and it requires detection of the platform at compile time. -- Function: int setcontext (const ucontext_t *UCP) Preliminary: | MT-Safe race:ucp | AS-Unsafe corrupt | AC-Unsafe corrupt | *Note POSIX Safety Concepts::. The ‘setcontext’ function restores the context described by UCP. The context is not modified and can be reused as often as wanted. If the context was created by ‘getcontext’ execution resumes with the registers filled with the same values and the same stack as if the ‘getcontext’ call just returned. If the context was modified with a call to ‘makecontext’ execution continues with the function passed to ‘makecontext’ which gets the specified parameters passed. If this function returns execution is resumed in the context which was referenced by the ‘uc_link’ element of the context structure passed to ‘makecontext’ at the time of the call. If ‘uc_link’ was a null pointer the application terminates normally with an exit status value of ‘EXIT_SUCCESS’ (*note Program Termination::). If the context was created by a call to a signal handler or from any other source then the behaviour of ‘setcontext’ is unspecified. Since the context contains information about the stack no two threads should use the same context at the same time. The result in most cases would be disastrous. The ‘setcontext’ function does not return unless an error occurred in which case it returns ‘-1’. The ‘setcontext’ function simply replaces the current context with the one described by the UCP parameter. This is often useful but there are situations where the current context has to be preserved. -- Function: int swapcontext (ucontext_t *restrict OUCP, const ucontext_t *restrict UCP) Preliminary: | MT-Safe race:oucp race:ucp | AS-Unsafe corrupt | AC-Unsafe corrupt | *Note POSIX Safety Concepts::. The ‘swapcontext’ function is similar to ‘setcontext’ but instead of just replacing the current context the latter is first saved in the object pointed to by OUCP as if this was a call to ‘getcontext’. The saved context would resume after the call to ‘swapcontext’. Once the current context is saved the context described in UCP is installed and execution continues as described in this context. If ‘swapcontext’ succeeds the function does not return unless the context OUCP is used without prior modification by ‘makecontext’. The return value in this case is ‘0’. If the function fails it returns ‘-1’ and sets ‘errno’ accordingly. Example for SVID Context Handling ================================= The easiest way to use the context handling functions is as a replacement for ‘setjmp’ and ‘longjmp’. The context contains on most platforms more information which may lead to fewer surprises but this also means using these functions is more expensive (besides being less portable). int random_search (int n, int (*fp) (int, ucontext_t *)) { volatile int cnt = 0; ucontext_t uc; /* Safe current context. */ if (getcontext (&uc) < 0) return -1; /* If we have not tried N times try again. */ if (cnt++ < n) /* Call the function with a new random number and the context. */ if (fp (rand (), &uc) != 0) /* We found what we were looking for. */ return 1; /* Not found. */ return 0; } Using contexts in such a way enables emulating exception handling. The search functions passed in the FP parameter could be very large, nested, and complex which would make it complicated (or at least would require a lot of code) to leave the function with an error value which has to be passed down to the caller. By using the context it is possible to leave the search function in one step and allow restarting the search which also has the nice side effect that it can be significantly faster. Something which is harder to implement with ‘setjmp’ and ‘longjmp’ is to switch temporarily to a different execution path and then resume where execution was stopped. #include #include #include #include #include /* Set by the signal handler. */ static volatile int expired; /* The contexts. */ static ucontext_t uc[3]; /* We do only a certain number of switches. */ static int switches; /* This is the function doing the work. It is just a skeleton, real code has to be filled in. */ static void f (int n) { int m = 0; while (1) { /* This is where the work would be done. */ if (++m % 100 == 0) { putchar ('.'); fflush (stdout); } /* Regularly the EXPIRE variable must be checked. */ if (expired) { /* We do not want the program to run forever. */ if (++switches == 20) return; printf ("\nswitching from %d to %d\n", n, 3 - n); expired = 0; /* Switch to the other context, saving the current one. */ swapcontext (&uc[n], &uc[3 - n]); } } } /* This is the signal handler which simply set the variable. */ void handler (int signal) { expired = 1; } int main (void) { struct sigaction sa; struct itimerval it; char st1[8192]; char st2[8192]; /* Initialize the data structures for the interval timer. */ sa.sa_flags = SA_RESTART; sigfillset (&sa.sa_mask); sa.sa_handler = handler; it.it_interval.tv_sec = 0; it.it_interval.tv_usec = 1; it.it_value = it.it_interval; /* Install the timer and get the context we can manipulate. */ if (sigaction (SIGPROF, &sa, NULL) < 0 || setitimer (ITIMER_PROF, &it, NULL) < 0 || getcontext (&uc[1]) == -1 || getcontext (&uc[2]) == -1) abort (); /* Create a context with a separate stack which causes the function ‘f’ to be call with the parameter ‘1’. Note that the ‘uc_link’ points to the main context which will cause the program to terminate once the function return. */ uc[1].uc_link = &uc[0]; uc[1].uc_stack.ss_sp = st1; uc[1].uc_stack.ss_size = sizeof st1; makecontext (&uc[1], (void (*) (void)) f, 1, 1); /* Similarly, but ‘2’ is passed as the parameter to ‘f’. */ uc[2].uc_link = &uc[0]; uc[2].uc_stack.ss_sp = st2; uc[2].uc_stack.ss_size = sizeof st2; makecontext (&uc[2], (void (*) (void)) f, 1, 2); /* Start running. */ swapcontext (&uc[0], &uc[1]); putchar ('\n'); return 0; } This an example how the context functions can be used to implement co-routines or cooperative multi-threading. All that has to be done is to call every once in a while ‘swapcontext’ to continue running a different context. It is not recommended to do the context switching from the signal handler directly since leaving the signal handler via ‘setcontext’ if the signal was delivered during code that was not asynchronous signal safe could lead to problems. Setting a variable in the signal handler and checking it in the body of the functions which are executed is a safer approach. Since ‘swapcontext’ is saving the current context it is possible to have multiple different scheduling points in the code. Execution will always resume where it was left.  File: libc.info, Node: Signal Handling, Next: Program Basics, Prev: Non-Local Exits, Up: Top 24 Signal Handling ****************** A "signal" is a software interrupt delivered to a process. The operating system uses signals to report exceptional situations to an executing program. Some signals report errors such as references to invalid memory addresses; others report asynchronous events, such as disconnection of a phone line. The GNU C Library defines a variety of signal types, each for a particular kind of event. Some kinds of events make it inadvisable or impossible for the program to proceed as usual, and the corresponding signals normally abort the program. Other kinds of signals that report harmless events are ignored by default. If you anticipate an event that causes signals, you can define a handler function and tell the operating system to run it when that particular type of signal arrives. Finally, one process can send a signal to another process; this allows a parent process to abort a child, or two related processes to communicate and synchronize. * Menu: * Concepts of Signals:: Introduction to the signal facilities. * Standard Signals:: Particular kinds of signals with standard names and meanings. * Signal Actions:: Specifying what happens when a particular signal is delivered. * Defining Handlers:: How to write a signal handler function. * Interrupted Primitives:: Signal handlers affect use of ‘open’, ‘read’, ‘write’ and other functions. * Generating Signals:: How to send a signal to a process. * Blocking Signals:: Making the system hold signals temporarily. * Waiting for a Signal:: Suspending your program until a signal arrives. * Signal Stack:: Using a Separate Signal Stack. * BSD Signal Handling:: Additional functions for backward compatibility with BSD.