ax_prototype
============

Synopsis
********

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

Description
***********

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 configure.in

      AX_PROTOTYPE(...)

2) call autoheader to see which symbols are not covered

3) add the lines in acconfig.h

      /* Type of Nth argument of function */
      #undef FUNCTION_ARGN

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

Complete example:

1) configure.in

      AX_PROTOTYPE(getpeername,
      [
       #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 */
      #undef GETPEERNAME_ARG2

      /* Type of third argument of getpeername */
      #undef GETPEERNAME_ARG3

4) in the code

       ...
       GETPEERNAME_ARG2 name;
       GETPEERNAME_ARG3 namelen;
       ...
       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 (http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_prototype.m4) or browse the macro's revision history (http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=history;f=m4/ax_prototype.m4).

License
*******

Copyright © 2009 Loic Dachary loic@senga.org

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 <https://www.gnu.org/licenses/>.

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