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### 10.12 Convenience Functions

GDB also supplies some convenience functions. 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 GDB.

These functions do not require GDB to be configured with `Python` support, which means that they are always available.

`$_isvoid (expr)`

  Return one if the expression expr is `void`. Otherwise it returns zero.

  A `void` expression is an expression where the type of the result is `void`. For example, you can examine a convenience variable (see Convenience Variables) to check whether it is `void`:

      (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

  In the example above, we used `$_isvoid` to check whether `$_exitcode` is `void` before and after the execution of the program being debugged. Before the execution there is no exit code to be examined, therefore `$_exitcode` is `void`. After the execution the program being debugged returned zero, therefore `$_exitcode` is zero, which means that it is not `void` anymore.

  The `void` expression can also be a call of a function from the program being debugged. For example, given the following function:

      void
      foo (void)
      {
      }

  The result of calling it inside GDB is `void`:

      (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

These functions require GDB to be configured with `Python` support.

`$_memeq(buf1, buf2, length)`

  Returns one if the length bytes at the addresses given by buf1 and buf2 are equal. Otherwise it returns zero.

`$_regex(str, regex)`

  Returns one if the string str matches the regular expression regex. Otherwise it returns zero. The syntax of the regular expression is that specified by `Python`’s regular expression support.

`$_streq(str1, str2)`

  Returns one if the strings str1 and str2 are equal. Otherwise it returns zero.

`$_strlen(str)`

  Returns the length of string str.

`$_caller_is(name[, number_of_frames])`

  Returns one if the calling function’s name is equal to name. Otherwise it returns zero.

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

  Example:

      (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

`$_caller_matches(regexp[, number_of_frames])`

  Returns one if the calling function’s name matches the regular expression regexp. Otherwise it returns zero.

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

`$_any_caller_is(name[, number_of_frames])`

  Returns one if any calling function’s name is equal to name. Otherwise it returns zero.

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

  This function differs from `$_caller_is` in that this function checks all stack frames from the immediate caller to the frame specified by number_of_frames, whereas `$_caller_is` only checks the frame specified by number_of_frames.

`$_any_caller_matches(regexp[, number_of_frames])`

  Returns one if any calling function’s name matches the regular expression regexp. Otherwise it returns zero.

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

  This function differs from `$_caller_matches` in that this function checks all stack frames from the immediate caller to the frame specified by number_of_frames, whereas `$_caller_matches` only checks the frame specified by number_of_frames.

`$_as_string(value)`

  Return the string representation of value.

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

      (gdb) printf "Visiting node of type %s\n", $_as_string(node)
      Visiting node of type NODE_INTEGER

GDB provides the ability to list and get help on convenience functions.

`help function`

  Print a list of all convenience functions.

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