ac_prototype

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 configure.in

  AC_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

  AC_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.

AC_DEFUN([AC_PROTOTYPE],[
dnl
dnl Upper case function name
dnl
 pushdef([function],translit([$1], [a-z], [A-Z]))
dnl
dnl Collect tags that will be substituted
dnl
 pushdef([tags],[AC_PROTOTYPE_TAGS(builtin([shift],builtin([shift],builtin([shift],$@))))])
dnl
dnl Wrap in a 1 time loop, when a combination is found break to stop the combinatory exploration
dnl
 for i in 1
 do
   AC_PROTOTYPE_LOOP(AC_PROTOTYPE_REVERSE($1, AC_PROTOTYPE_SUBST($2,tags),AC_PROTOTYPE_SUBST($3,tags),builtin([shift],builtin([shift],builtin([shift],$@)))))
   AC_MSG_ERROR($1 unable to find a working combination)
 done
 popdef([tags])
 popdef([function])
])

dnl
dnl AC_PROTOTYPE_REVERSE(list)
dnl
dnl Reverse the order of the <list>
dnl
AC_DEFUN([AC_PROTOTYPE_REVERSE],[ifelse($#,0,,$#,1,[[$1]],[AC_PROTOTYPE_REVERSE(builtin([shift],$@)),[$1]])])

dnl
dnl AC_PROTOTYPE_SUBST(string, tag)
dnl
dnl Substitute all occurence of <tag> in <string> with <tag>_VAL.
dnl Assumes that tag_VAL is a macro containing the value associated to tag.
dnl
AC_DEFUN([AC_PROTOTYPE_SUBST],[ifelse($2,,[$1],[AC_PROTOTYPE_SUBST(patsubst([$1],[$2],[$2[]_VAL]),builtin([shift],builtin([shift],$@)))])])

dnl
dnl AC_PROTOTYPE_TAGS([tag, values, [tag, values ...]])
dnl
dnl Generate a list of <tag> by skipping <values>.
dnl
AC_DEFUN([AC_PROTOTYPE_TAGS],[ifelse($1,,[],[$1, AC_PROTOTYPE_TAGS(builtin([shift],builtin([shift],$@)))])])

dnl
dnl AC_PROTOTYPE_DEFINES(tags)
dnl
dnl Generate a AC_DEFINE(function_tag, tag_VAL) for each tag in <tags> list
dnl Assumes that function is a macro containing the name of the function in upper case
dnl and that tag_VAL is a macro containing the value associated to tag.
dnl
AC_DEFUN([AC_PROTOTYPE_DEFINES],[ifelse($1,,[],[AC_DEFINE(function[]_$1, $1_VAL) AC_PROTOTYPE_DEFINES(builtin([shift],$@))])])

dnl
dnl AC_PROTOTYPE_STATUS(tags)
dnl
dnl Generates a message suitable for argument to AC_MSG_* macros. For each tag
dnl in the <tags> list the message tag => tag_VAL is generated.
dnl Assumes that tag_VAL is a macro containing the value associated to tag.
dnl
AC_DEFUN([AC_PROTOTYPE_STATUS],[ifelse($1,,[],[$1 => $1_VAL AC_PROTOTYPE_STATUS(builtin([shift],$@))])])

dnl
dnl AC_PROTOTYPE_EACH(tag, values)
dnl
dnl Call AC_PROTOTYPE_LOOP for each values and define the macro tag_VAL to
dnl the current value.
dnl
AC_DEFUN([AC_PROTOTYPE_EACH],[
  ifelse($2,, [
  ], [
    pushdef([$1_VAL], $2)
    AC_PROTOTYPE_LOOP(rest)
    popdef([$1_VAL])
    AC_PROTOTYPE_EACH($1, builtin([shift], builtin([shift], $@)))
  ])
])

dnl
dnl AC_PROTOTYPE_LOOP([tag, values, [tag, values ...]], code, include, function)
dnl
dnl If there is a tag/values pair, call AC_PROTOTYPE_EACH with it.
dnl If there is no tag/values pair left, tries to compile the code and include
dnl using AC_TRY_COMPILE. If it compiles, AC_DEFINE all the tags to their
dnl current value and exit with success.
dnl
AC_DEFUN([AC_PROTOTYPE_LOOP],[
 ifelse(builtin([eval], $# > 3), 1,
   [
     pushdef([rest],[builtin([shift],builtin([shift],$@))])
     AC_PROTOTYPE_EACH($2,$1)
     popdef([rest])
   ], [
     AC_MSG_CHECKING($3 AC_PROTOTYPE_STATUS(tags))
dnl
dnl Activate fatal warnings if possible, gives better guess
dnl
     ac_save_CPPFLAGS="$CPPFLAGS"
     ifelse(AC_LANG,CPLUSPLUS,if test "$GXX" = "yes" ; then CPPFLAGS="$CPPFLAGS -Werror" ; fi)
     ifelse(AC_LANG,C,if test "$GCC" = "yes" ; then CPPFLAGS="$CPPFLAGS -Werror" ; fi)
     AC_TRY_COMPILE($2, $1, [
      CPPFLAGS="$ac_save_CPPFLAGS"
      AC_MSG_RESULT(ok)
      AC_PROTOTYPE_DEFINES(tags)
      break;
     ], [
      CPPFLAGS="$ac_save_CPPFLAGS"
      AC_MSG_RESULT(not ok)
     ])
   ]
 )
])