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   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 successfull 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 successfull 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

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