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<title>Debugging with GDB: Convenience Funs</title>
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<a name="Convenience-Funs"></a>
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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="prev">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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<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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$4 = 1
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</pre></div>
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</dd>
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</dl>
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<p>These functions require <small>GDB</small> to be configured with
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<code>Python</code> support.
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</p>
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<dl compact="compact">
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<dt><code>$_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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</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="prev">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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