379 lines
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379 lines
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<title>Debugging with GDB: Convenience Funs</title>
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Data.html#Data" rel="up" title="Data">
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<link href="Registers.html#Registers" rel="next" title="Registers">
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Convenience-Funs"></a>
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<div class="header">
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<p>
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Next: <a href="Registers.html#Registers" accesskey="n" rel="next">Registers</a>, Previous: <a href="Convenience-Vars.html#Convenience-Vars" accesskey="p" rel="previous">Convenience Vars</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Convenience-Functions"></a>
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<h3 class="section">10.12 Convenience Functions</h3>
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<a name="index-convenience-functions"></a>
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<p><small>GDB</small> also supplies some <em>convenience functions</em>. These
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have a syntax similar to convenience variables. A convenience
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function can be used in an expression just like an ordinary function;
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however, a convenience function is implemented internally to
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<small>GDB</small>.
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</p>
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<p>These functions do not require <small>GDB</small> to be configured with
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<code>Python</code> support, which means that they are always available.
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</p>
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<dl compact="compact">
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<dt><code>$_isvoid (<var>expr</var>)</code></dt>
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<dd><a name="index-_0024_005fisvoid_002c-convenience-function"></a>
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<p>Return one if the expression <var>expr</var> is <code>void</code>. Otherwise it
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returns zero.
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</p>
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<p>A <code>void</code> expression is an expression where the type of the result
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is <code>void</code>. For example, you can examine a convenience variable
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(see <a href="Convenience-Vars.html#Convenience-Vars">Convenience Variables</a>) to check whether
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it is <code>void</code>:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print $_exitcode
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$1 = void
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(gdb) print $_isvoid ($_exitcode)
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$2 = 1
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(gdb) run
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Starting program: ./a.out
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[Inferior 1 (process 29572) exited normally]
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(gdb) print $_exitcode
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$3 = 0
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(gdb) print $_isvoid ($_exitcode)
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$4 = 0
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</pre></div>
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<p>In the example above, we used <code>$_isvoid</code> to check whether
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<code>$_exitcode</code> is <code>void</code> before and after the execution of the
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program being debugged. Before the execution there is no exit code to
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be examined, therefore <code>$_exitcode</code> is <code>void</code>. After the
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execution the program being debugged returned zero, therefore
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<code>$_exitcode</code> is zero, which means that it is not <code>void</code>
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anymore.
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</p>
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<p>The <code>void</code> expression can also be a call of a function from the
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program being debugged. For example, given the following function:
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</p>
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<div class="smallexample">
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<pre class="smallexample">void
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foo (void)
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{
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}
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</pre></div>
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<p>The result of calling it inside <small>GDB</small> is <code>void</code>:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print foo ()
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$1 = void
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(gdb) print $_isvoid (foo ())
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$2 = 1
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(gdb) set $v = foo ()
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(gdb) print $v
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$3 = void
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(gdb) print $_isvoid ($v)
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$4 = 1
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</pre></div>
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</dd>
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<dt><code>$_gdb_setting_str (<var>setting</var>)</code></dt>
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<dd><a name="index-_0024_005fgdb_005fsetting_005fstr_002c-convenience-function"></a>
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<p>Return the value of the <small>GDB</small> <var>setting</var> as a string.
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<var>setting</var> is any setting that can be used in a <code>set</code> or
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<code>show</code> command (see <a href="Controlling-GDB.html#Controlling-GDB">Controlling GDB</a>).
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) show print frame-arguments
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Printing of non-scalar frame arguments is "scalars".
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(gdb) p $_gdb_setting_str("print frame-arguments")
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$1 = "scalars"
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(gdb) p $_gdb_setting_str("height")
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$2 = "30"
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(gdb)
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</pre></div>
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</dd>
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<dt><code>$_gdb_setting (<var>setting</var>)</code></dt>
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<dd><a name="index-_0024_005fgdb_005fsetting_002c-convenience-function"></a>
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<p>Return the value of the <small>GDB</small> <var>setting</var>.
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The type of the returned value depends on the setting.
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</p>
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<p>The value type for boolean and auto boolean settings is <code>int</code>.
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The boolean values <code>off</code> and <code>on</code> are converted to
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the integer values <code>0</code> and <code>1</code>. The value <code>auto</code> is
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converted to the value <code>-1</code>.
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</p>
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<p>The value type for integer settings is either <code>unsigned int</code>
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or <code>int</code>, depending on the setting.
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</p>
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<p>Some integer settings accept an <code>unlimited</code> value.
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Depending on the setting, the <code>set</code> command also accepts
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the value <code>0</code> or the value <code>-1</code> as a synonym for
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<code>unlimited</code>.
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For example, <code>set height unlimited</code> is equivalent to
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<code>set height 0</code>.
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</p>
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<p>Some other settings that accept the <code>unlimited</code> value
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use the value <code>0</code> to literally mean zero.
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For example, <code>set history size 0</code> indicates to not
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record any <small>GDB</small> commands in the command history.
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For such settings, <code>-1</code> is the synonym
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for <code>unlimited</code>.
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</p>
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<p>See the documentation of the corresponding <code>set</code> command for
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the numerical value equivalent to <code>unlimited</code>.
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</p>
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<p>The <code>$_gdb_setting</code> function converts the unlimited value
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to a <code>0</code> or a <code>-1</code> value according to what the
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<code>set</code> command uses.
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) p $_gdb_setting_str("height")
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$1 = "30"
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(gdb) p $_gdb_setting("height")
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$2 = 30
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(gdb) set height unlimited
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(gdb) p $_gdb_setting_str("height")
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$3 = "unlimited"
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(gdb) p $_gdb_setting("height")
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$4 = 0
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</pre><pre class="smallexample">(gdb) p $_gdb_setting_str("history size")
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$5 = "unlimited"
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(gdb) p $_gdb_setting("history size")
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$6 = -1
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(gdb) p $_gdb_setting_str("disassemble-next-line")
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$7 = "auto"
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(gdb) p $_gdb_setting("disassemble-next-line")
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$8 = -1
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(gdb)
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</pre></div>
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<p>Other setting types (enum, filename, optional filename, string, string noescape)
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are returned as string values.
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</p>
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</dd>
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<dt><code>$_gdb_maint_setting_str (<var>setting</var>)</code></dt>
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<dd><a name="index-_0024_005fgdb_005fmaint_005fsetting_005fstr_002c-convenience-function"></a>
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<p>Like the <code>$_gdb_setting_str</code> function, but works with
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<code>maintenance set</code> variables.
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</p>
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</dd>
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<dt><code>$_gdb_maint_setting (<var>setting</var>)</code></dt>
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<dd><a name="index-_0024_005fgdb_005fmaint_005fsetting_002c-convenience-function"></a>
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<p>Like the <code>$_gdb_setting</code> function, but works with
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<code>maintenance set</code> variables.
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</p>
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</dd>
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</dl>
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<p>The following functions require <small>GDB</small> to be configured with
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<code>Python</code> support.
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</p>
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<dl compact="compact">
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<dt><code>$_memeq(<var>buf1</var>, <var>buf2</var>, <var>length</var>)</code></dt>
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<dd><a name="index-_0024_005fmemeq_002c-convenience-function"></a>
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<p>Returns one if the <var>length</var> bytes at the addresses given by
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<var>buf1</var> and <var>buf2</var> are equal.
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Otherwise it returns zero.
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</p>
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</dd>
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<dt><code>$_regex(<var>str</var>, <var>regex</var>)</code></dt>
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<dd><a name="index-_0024_005fregex_002c-convenience-function"></a>
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<p>Returns one if the string <var>str</var> matches the regular expression
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<var>regex</var>. Otherwise it returns zero.
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The syntax of the regular expression is that specified by <code>Python</code>’s
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regular expression support.
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</p>
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</dd>
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<dt><code>$_streq(<var>str1</var>, <var>str2</var>)</code></dt>
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<dd><a name="index-_0024_005fstreq_002c-convenience-function"></a>
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<p>Returns one if the strings <var>str1</var> and <var>str2</var> are equal.
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Otherwise it returns zero.
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</p>
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</dd>
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<dt><code>$_strlen(<var>str</var>)</code></dt>
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<dd><a name="index-_0024_005fstrlen_002c-convenience-function"></a>
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<p>Returns the length of string <var>str</var>.
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</p>
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</dd>
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<dt><code>$_caller_is(<var>name</var><span class="roman">[</span>, <var>number_of_frames</var><span class="roman">]</span>)</code></dt>
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<dd><a name="index-_0024_005fcaller_005fis_002c-convenience-function"></a>
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<p>Returns one if the calling function’s name is equal to <var>name</var>.
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Otherwise it returns zero.
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</p>
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<p>If the optional argument <var>number_of_frames</var> is provided,
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it is the number of frames up in the stack to look.
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The default is 1.
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</p>
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<p>Example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) backtrace
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#0 bottom_func ()
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at testsuite/gdb.python/py-caller-is.c:21
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#1 0x00000000004005a0 in middle_func ()
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at testsuite/gdb.python/py-caller-is.c:27
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#2 0x00000000004005ab in top_func ()
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at testsuite/gdb.python/py-caller-is.c:33
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#3 0x00000000004005b6 in main ()
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at testsuite/gdb.python/py-caller-is.c:39
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(gdb) print $_caller_is ("middle_func")
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$1 = 1
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(gdb) print $_caller_is ("top_func", 2)
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$1 = 1
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</pre></div>
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</dd>
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<dt><code>$_caller_matches(<var>regexp</var><span class="roman">[</span>, <var>number_of_frames</var><span class="roman">]</span>)</code></dt>
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<dd><a name="index-_0024_005fcaller_005fmatches_002c-convenience-function"></a>
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<p>Returns one if the calling function’s name matches the regular expression
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<var>regexp</var>. Otherwise it returns zero.
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</p>
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<p>If the optional argument <var>number_of_frames</var> is provided,
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it is the number of frames up in the stack to look.
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The default is 1.
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</p>
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</dd>
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<dt><code>$_any_caller_is(<var>name</var><span class="roman">[</span>, <var>number_of_frames</var><span class="roman">]</span>)</code></dt>
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<dd><a name="index-_0024_005fany_005fcaller_005fis_002c-convenience-function"></a>
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<p>Returns one if any calling function’s name is equal to <var>name</var>.
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Otherwise it returns zero.
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</p>
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<p>If the optional argument <var>number_of_frames</var> is provided,
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it is the number of frames up in the stack to look.
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The default is 1.
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</p>
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<p>This function differs from <code>$_caller_is</code> in that this function
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checks all stack frames from the immediate caller to the frame specified
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by <var>number_of_frames</var>, whereas <code>$_caller_is</code> only checks the
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frame specified by <var>number_of_frames</var>.
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</p>
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</dd>
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<dt><code>$_any_caller_matches(<var>regexp</var><span class="roman">[</span>, <var>number_of_frames</var><span class="roman">]</span>)</code></dt>
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<dd><a name="index-_0024_005fany_005fcaller_005fmatches_002c-convenience-function"></a>
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<p>Returns one if any calling function’s name matches the regular expression
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<var>regexp</var>. Otherwise it returns zero.
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</p>
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<p>If the optional argument <var>number_of_frames</var> is provided,
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it is the number of frames up in the stack to look.
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The default is 1.
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</p>
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<p>This function differs from <code>$_caller_matches</code> in that this function
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checks all stack frames from the immediate caller to the frame specified
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by <var>number_of_frames</var>, whereas <code>$_caller_matches</code> only checks the
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frame specified by <var>number_of_frames</var>.
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</p>
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</dd>
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<dt><code>$_as_string(<var>value</var>)</code></dt>
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<dd><a name="index-_0024_005fas_005fstring_002c-convenience-function"></a>
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<p>Return the string representation of <var>value</var>.
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</p>
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<p>This function is useful to obtain the textual label (enumerator) of an
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enumeration value. For example, assuming the variable <var>node</var> is of
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an enumerated type:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) printf "Visiting node of type %s\n", $_as_string(node)
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Visiting node of type NODE_INTEGER
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</pre></div>
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</dd>
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<dt><code>$_cimag(<var>value</var>)</code></dt>
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<dt><code>$_creal(<var>value</var>)</code></dt>
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<dd><a name="index-_0024_005fcimag_002c-convenience-function"></a>
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<a name="index-_0024_005fcreal_002c-convenience-function"></a>
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<p>Return the imaginary (<code>$_cimag</code>) or real (<code>$_creal</code>) part of
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the complex number <var>value</var>.
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</p>
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<p>The type of the imaginary or real part depends on the type of the
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complex number, e.g., using <code>$_cimag</code> on a <code>float complex</code>
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will return an imaginary part of type <code>float</code>.
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</p>
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</dd>
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</dl>
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<p><small>GDB</small> provides the ability to list and get help on
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convenience functions.
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</p>
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<dl compact="compact">
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<dt><code>help function</code></dt>
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<dd><a name="index-help-function"></a>
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<a name="index-show-all-convenience-functions"></a>
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<p>Print a list of all convenience functions.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Registers.html#Registers" accesskey="n" rel="next">Registers</a>, Previous: <a href="Convenience-Vars.html#Convenience-Vars" accesskey="p" rel="previous">Convenience Vars</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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