<html lang="en">
<head>
<title>Convenience Funs - Debugging with GDB</title>
<meta http-equiv="Content-Type" content="text/html">
<meta name="description" content="Debugging with GDB">
<meta name="generator" content="makeinfo 4.13">
<link title="Top" rel="start" href="index.html#Top">
<link rel="up" href="Data.html#Data" title="Data">
<link rel="prev" href="Convenience-Vars.html#Convenience-Vars" title="Convenience Vars">
<link rel="next" href="Registers.html#Registers" title="Registers">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
Copyright (C) 1988-2019 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'' and ``Free Software Needs
Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
and with the Back-Cover Texts as in (a) below.

(a) The FSF's Back-Cover Text is: ``You are free to copy and modify
this GNU Manual.  Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom.''
-->
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
  pre.display { font-family:inherit }
  pre.format  { font-family:inherit }
  pre.smalldisplay { font-family:inherit; font-size:smaller }
  pre.smallformat  { font-family:inherit; font-size:smaller }
  pre.smallexample { font-size:smaller }
  pre.smalllisp    { font-size:smaller }
  span.sc    { font-variant:small-caps }
  span.roman { font-family:serif; font-weight:normal; } 
  span.sansserif { font-family:sans-serif; font-weight:normal; } 
--></style>
</head>
<body>
<div class="node">
<a name="Convenience-Funs"></a>
<p>
Next:&nbsp;<a rel="next" accesskey="n" href="Registers.html#Registers">Registers</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="Convenience-Vars.html#Convenience-Vars">Convenience Vars</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="Data.html#Data">Data</a>
<hr>
</div>

<h3 class="section">10.12 Convenience Functions</h3>

<p><a name="index-convenience-functions-736"></a><span class="sc">gdb</span> also supplies some <dfn>convenience functions</dfn>.  These
have a syntax similar to convenience variables.  A convenience
function can be used in an expression just like an ordinary function;
however, a convenience function is implemented internally to
<span class="sc">gdb</span>.

   <p>These functions do not require <span class="sc">gdb</span> to be configured with
<code>Python</code> support, which means that they are always available.

     <dl>
<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
returns zero.

     <p>A <code>void</code> expression is an expression where the type of the result
is <code>void</code>.  For example, you can examine a convenience variable
(see <a href="Convenience-Vars.html#Convenience-Vars">Convenience Variables</a>) to check whether
it is <code>void</code>:

     <pre class="smallexample">          (gdb) print $_exitcode
          $1 = void
          (gdb) print $_isvoid ($_exitcode)
          $2 = 1
          (gdb) run
          Starting program: ./a.out
          [Inferior 1 (process 29572) exited normally]
          (gdb) print $_exitcode
          $3 = 0
          (gdb) print $_isvoid ($_exitcode)
          $4 = 0
</pre>
     <p>In the example above, we used <code>$_isvoid</code> to check whether
<code>$_exitcode</code> is <code>void</code> before and after the execution of the
program being debugged.  Before the execution there is no exit code to
be examined, therefore <code>$_exitcode</code> is <code>void</code>.  After the
execution the program being debugged returned zero, therefore
<code>$_exitcode</code> is zero, which means that it is not <code>void</code>
anymore.

     <p>The <code>void</code> expression can also be a call of a function from the
program being debugged.  For example, given the following function:

     <pre class="smallexample">          void
          foo (void)
          {
          }
</pre>
     <p>The result of calling it inside <span class="sc">gdb</span> is <code>void</code>:

     <pre class="smallexample">          (gdb) print foo ()
          $1 = void
          (gdb) print $_isvoid (foo ())
          $2 = 1
          (gdb) set $v = foo ()
          (gdb) print $v
          $3 = void
          (gdb) print $_isvoid ($v)
          $4 = 1
</pre>
     </dl>

   <p>These functions require <span class="sc">gdb</span> to be configured with
<code>Python</code> support.

     <dl>
<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
<var>buf1</var> and <var>buf2</var> are equal. 
Otherwise it returns zero.

     <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
<var>regex</var>.  Otherwise it returns zero. 
The syntax of the regular expression is that specified by <code>Python</code>'s
regular expression support.

     <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. 
Otherwise it returns zero.

     <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>.

     <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>. 
Otherwise it returns zero.

     <p>If the optional argument <var>number_of_frames</var> is provided,
it is the number of frames up in the stack to look. 
The default is 1.

     <p>Example:

     <pre class="smallexample">          (gdb) backtrace
          #0  bottom_func ()
              at testsuite/gdb.python/py-caller-is.c:21
          #1  0x00000000004005a0 in middle_func ()
              at testsuite/gdb.python/py-caller-is.c:27
          #2  0x00000000004005ab in top_func ()
              at testsuite/gdb.python/py-caller-is.c:33
          #3  0x00000000004005b6 in main ()
              at testsuite/gdb.python/py-caller-is.c:39
          (gdb) print $_caller_is ("middle_func")
          $1 = 1
          (gdb) print $_caller_is ("top_func", 2)
          $1 = 1
</pre>
     <br><dt><code>$_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
<var>regexp</var>.  Otherwise it returns zero.

     <p>If the optional argument <var>number_of_frames</var> is provided,
it is the number of frames up in the stack to look. 
The default is 1.

     <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>. 
Otherwise it returns zero.

     <p>If the optional argument <var>number_of_frames</var> is provided,
it is the number of frames up in the stack to look. 
The default is 1.

     <p>This function differs from <code>$_caller_is</code> in that this function
checks all stack frames from the immediate caller to the frame specified
by <var>number_of_frames</var>, whereas <code>$_caller_is</code> only checks the
frame specified by <var>number_of_frames</var>.

     <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
<var>regexp</var>.  Otherwise it returns zero.

     <p>If the optional argument <var>number_of_frames</var> is provided,
it is the number of frames up in the stack to look. 
The default is 1.

     <p>This function differs from <code>$_caller_matches</code> in that this function
checks all stack frames from the immediate caller to the frame specified
by <var>number_of_frames</var>, whereas <code>$_caller_matches</code> only checks the
frame specified by <var>number_of_frames</var>.

     <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>.

     <p>This function is useful to obtain the textual label (enumerator) of an
enumeration value.  For example, assuming the variable <var>node</var> is of
an enumerated type:

     <pre class="smallexample">          (gdb) printf "Visiting node of type %s\n", $_as_string(node)
          Visiting node of type NODE_INTEGER
</pre>
     </dl>

   <p><span class="sc">gdb</span> provides the ability to list and get help on
convenience functions.

     <dl>
<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. 
</dl>

   </body></html>