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@node ax_prototype
@unnumberedsec ax_prototype
@majorheading Synopsis
@smallexample
AX_PROTOTYPE(function, includes, code, TAG1, values1 [, TAG2, values2 [...]])
@end smallexample
@majorheading 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 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
@smallexample
AX_PROTOTYPE(...)
@end smallexample
2) call autoheader to see which symbols are not covered
3) add the lines in acconfig.h
@smallexample
/* Type of Nth argument of function */
#undef FUNCTION_ARGN
@end smallexample
4) Within the code use FUNCTION_ARGN instead of an hardwired type
Complete example:
1) configure.in
@smallexample
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])
@end smallexample
2) call autoheader
@smallexample
autoheader: Symbol `GETPEERNAME_ARG2' is not covered by ./acconfig.h
autoheader: Symbol `GETPEERNAME_ARG3' is not covered by ./acconfig.h
@end smallexample
3) acconfig.h
@smallexample
/* Type of second argument of getpeername */
#undef GETPEERNAME_ARG2
@end smallexample
@smallexample
/* Type of third argument of getpeername */
#undef GETPEERNAME_ARG3
@end smallexample
4) in the code
@smallexample
...
GETPEERNAME_ARG2 name;
GETPEERNAME_ARG3 namelen;
...
ret = getpeername(socket, &name, &namelen);
...
@end smallexample
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.
@majorheading Source Code
Download the
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_prototype.m4,latest
version of @file{ax_prototype.m4}} or browse
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=history;f=m4/ax_prototype.m4,the
macro's revision history}.
@majorheading License
@w{Copyright @copyright{} 2009 Loic Dachary @email{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 <http://www.gnu.org/licenses/>.
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.
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