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203 lines
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<html lang="en">
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<title>Convenience Funs - Debugging with GDB</title>
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<link rel="up" href="Data.html#Data" title="Data">
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<link rel="prev" href="Convenience-Vars.html#Convenience-Vars" title="Convenience Vars">
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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</head>
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<body>
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<div class="node">
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<a name="Convenience-Funs"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Registers.html#Registers">Registers</a>,
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Previous: <a rel="previous" accesskey="p" href="Convenience-Vars.html#Convenience-Vars">Convenience Vars</a>,
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Up: <a rel="up" accesskey="u" href="Data.html#Data">Data</a>
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<hr>
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</div>
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<h3 class="section">10.12 Convenience Functions</h3>
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<p><a name="index-convenience-functions-736"></a><span class="sc">gdb</span> also supplies some <dfn>convenience functions</dfn>. 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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<span class="sc">gdb</span>.
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<p>These functions do not require <span class="sc">gdb</span> to be configured with
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<code>Python</code> support, which means that they are always available.
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<dl>
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<dt><code>$_isvoid (</code><var>expr</var><code>)</code><dd><a name="index-g_t_0024_005fisvoid_0040r_007b_002c-convenience-function_007d-737"></a>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>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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<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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$4 = 0
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</pre>
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<p>In the example above, we used <code>$_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>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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<pre class="smallexample"> void
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foo (void)
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{
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}
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</pre>
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<p>The result of calling it inside <span class="sc">gdb</span> is <code>void</code>:
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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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$4 = 1
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</pre>
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</dl>
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<p>These functions require <span class="sc">gdb</span> to be configured with
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<code>Python</code> support.
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<dl>
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<dt><code>$_memeq(</code><var>buf1</var><code>, </code><var>buf2</var><code>, </code><var>length</var><code>)</code><dd><a name="index-g_t_0024_005fmemeq_0040r_007b_002c-convenience-function_007d-738"></a>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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<br><dt><code>$_regex(</code><var>str</var><code>, </code><var>regex</var><code>)</code><dd><a name="index-g_t_0024_005fregex_0040r_007b_002c-convenience-function_007d-739"></a>Returns one if the string <var>str</var> matches the regular expression
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<var>regex</var>. Otherwise it returns zero.
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The syntax of the regular expression is that specified by <code>Python</code>'s
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regular expression support.
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<br><dt><code>$_streq(</code><var>str1</var><code>, </code><var>str2</var><code>)</code><dd><a name="index-g_t_0024_005fstreq_0040r_007b_002c-convenience-function_007d-740"></a>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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<br><dt><code>$_strlen(</code><var>str</var><code>)</code><dd><a name="index-g_t_0024_005fstrlen_0040r_007b_002c-convenience-function_007d-741"></a>Returns the length of string <var>str</var>.
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<br><dt><code>$_caller_is(</code><var>name</var><span class="roman">[</span><code>, </code><var>number_of_frames</var><span class="roman">]</span><code>)</code><dd><a name="index-g_t_0024_005fcaller_005fis_0040r_007b_002c-convenience-function_007d-742"></a>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>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>Example:
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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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$1 = 1
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</pre>
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<br><dt><code>$_caller_matches(</code><var>regexp</var><span class="roman">[</span><code>, </code><var>number_of_frames</var><span class="roman">]</span><code>)</code><dd><a name="index-g_t_0024_005fcaller_005fmatches_0040r_007b_002c-convenience-function_007d-743"></a>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>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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<br><dt><code>$_any_caller_is(</code><var>name</var><span class="roman">[</span><code>, </code><var>number_of_frames</var><span class="roman">]</span><code>)</code><dd><a name="index-g_t_0024_005fany_005fcaller_005fis_0040r_007b_002c-convenience-function_007d-744"></a>Returns one if any calling function's name is equal to <var>name</var>.
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Otherwise it returns zero.
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<p>If the optional argument <var>number_of_frames</var> is provided,
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it is the number of frames up in the stack to look.
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The default is 1.
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<p>This function differs from <code>$_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>$_caller_is</code> only checks the
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frame specified by <var>number_of_frames</var>.
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<br><dt><code>$_any_caller_matches(</code><var>regexp</var><span class="roman">[</span><code>, </code><var>number_of_frames</var><span class="roman">]</span><code>)</code><dd><a name="index-g_t_0024_005fany_005fcaller_005fmatches_0040r_007b_002c-convenience-function_007d-745"></a>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>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>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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<br><dt><code>$_as_string(</code><var>value</var><code>)</code><dd><a name="index-g_t_0024_005fas_005fstring_0040r_007b_002c-convenience-function_007d-746"></a>Return the string representation of <var>value</var>.
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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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<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>
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</dl>
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<p><span class="sc">gdb</span> provides the ability to list and get help on
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convenience functions.
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<dl>
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<dt><code>help function</code><dd><a name="index-help-function-747"></a><a name="index-show-all-convenience-functions-748"></a>Print a list of all convenience functions.
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</dl>
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</body></html>
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