Next: , Previous: , Up: The Macros  



   AX_PROTOTYPE(function, includes, code, TAG1, values1 [, TAG2, values2 [...]])


Try all the combinations of <TAG1>, <TAG2>... to successfully compile <code>. <TAG1>, <TAG2>, ... are substituted in <code> and <include> with values found in <values1>, <values2>, ... respectively. <values1>, <values2>, ... contain a list of possible values for each corresponding tag and all combinations are tested. When AC_TRY_COMPILE(include, code) is successful for a given substitution, the macro stops and defines the following macros: FUNCTION_TAG1, FUNCTION_TAG2, ... using AC_DEFINE() with values set to the current values of <TAG1>, <TAG2>, ... If no combination is successful the configure script is aborted with a message.

Intended purpose is to find which combination of argument types is acceptable for a given function <function>. It is recommended to list the most specific types first. For instance ARG1, [size_t, int] instead of ARG1, [int, size_t].

Generic usage pattern:

1) add a call in


2) call autoheader to see which symbols are not covered

3) add the lines in acconfig.h

 /* Type of Nth argument of function */

4) Within the code use FUNCTION_ARGN instead of an hardwired type

Complete example:


  #include <sys/types.h>
  #include <sys/socket.h>
  int a = 0;
  ARG2 * b = 0;
  ARG3 * c = 0;
  getpeername(a, b, c);
 ARG2, [struct sockaddr, void],
 ARG3, [socklen_t, size_t, int, unsigned int, long unsigned int])

2) call autoheader

   autoheader: Symbol `GETPEERNAME_ARG2' is not covered by ./acconfig.h
 autoheader: Symbol `GETPEERNAME_ARG3' is not covered by ./acconfig.h

3) acconfig.h

 /* Type of second argument of getpeername */
 /* Type of third argument of getpeername */

4) in the code

  ret = getpeername(socket, &name, &namelen);

Implementation notes: generating all possible permutations of the arguments is not easily done with the usual mixture of shell and m4, that is why this macro is almost 100% m4 code. It generates long but simple to read code.

Source Code

Download the latest version of ax_prototype.m4 or browse the macro’s revision history.


Copyright © 2009 Loic Dachary

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see <>.

As a special exception, the respective Autoconf Macro’s copyright owner gives unlimited permission to copy, distribute and modify the configure scripts that are the output of Autoconf when processing the Macro. You need not follow the terms of the GNU General Public License when using or distributing such scripts, even though portions of the text of the Macro appear in them. The GNU General Public License (GPL) does govern all other use of the material that constitutes the Autoconf Macro.

This special exception to the GPL applies to versions of the Autoconf Macro released by the Autoconf Archive. When you make and distribute a modified version of the Autoconf Macro, you may extend this special exception to the GPL to apply to your modified version as well.

Next: , Previous: , Up: The Macros