Re: how to test for a prototype difference

[Philip Herron]

Awh cool thanks for sharing that i couldn't figure out how to do this
with something in work.

On 1 May 2014 01:51, Eric Blake <address@hidden> wrote:
> On 04/30/2014 06:12 PM, Thomas Klausner wrote:
>> Hi!
>>
>> I found out that the prototypes for backtrace() and backtrace_symbol()
>> differ on some operating systems.
>>
>
>>
>> The main difference is that on NetBSD, size_t is used for most
>> arguments that are int on the other systems; also,
>> backtrace_symbols_fd returns an int.
>>
>> I'd like to test for the difference int <-> size_t in a configure
>> script so I can get integer type/sign conversion-warnings free code on
>> all these operating systems.
>>
>> I'm however not sure how to do this. Does anyone have a suggestion?
>
> Yep - use function pointer assignment or redeclaration to force the
> compiler to complain if the redeclaration used the wrong type.  Gnulib
> has some examples; here's one with ioctl(), which on Linux takes an
> 'unsigned long' instead of the POSIX 'int' for the second parameter:
>
>     AC_CACHE_CHECK([for ioctl with POSIX signature],
>       [gl_cv_func_ioctl_posix_signature],
>       [AC_COMPILE_IFELSE(
>          [AC_LANG_PROGRAM(
>             [[#include <sys/ioctl.h>]],
>             [[extern
>               #ifdef __cplusplus
>               "C"
>               #endif
>               int ioctl (int, int, ...);
>             ]])
>          ],
>          [gl_cv_func_ioctl_posix_signature=yes],
>          [gl_cv_func_ioctl_posix_signature=no])
>       ])
>     if test $gl_cv_func_ioctl_posix_signature != yes; then
>       REPLACE_IOCTL=1
>     fi
>
> Or this one originally from gettext (but annoyingly encroaching on
> automake's namespace), checking whether iconv() uses a const or not:
>
>     AC_MSG_CHECKING([for iconv declaration])
>     AC_CACHE_VAL([am_cv_proto_iconv], [
>       AC_COMPILE_IFELSE(
>         [AC_LANG_PROGRAM(
>            [[
> #include <stdlib.h>
> #include <iconv.h>
> extern
> #ifdef __cplusplus
> "C"
> #endif
> #if defined(__STDC__) || defined(_MSC_VER) || defined(__cplusplus)
> size_t iconv (iconv_t cd, char * *inbuf, size_t *inbytesleft, char *
> *outbuf, size_t *outbytesleft);
> #else
> size_t iconv();
> #endif
>            ]],
>            [[]])],
>         [am_cv_proto_iconv_arg1=""],
>         [am_cv_proto_iconv_arg1="const"])
>       am_cv_proto_iconv="extern size_t iconv (iconv_t cd,
> $am_cv_proto_iconv_arg1 char * *inbuf, size_t *inbytesleft, char *
> *outbuf, size_t *outbytesleft);"])
>     am_cv_proto_iconv=`echo "[$]am_cv_proto_iconv" | tr -s ' ' | sed -e
> 's/( /(/'`
>     AC_MSG_RESULT([
>          $am_cv_proto_iconv])
>     AC_DEFINE_UNQUOTED([ICONV_CONST], [$am_cv_proto_iconv_arg1],
>       [Define as const if the declaration of iconv() needs const.])
>
> Hopefully that gives you some ideas.
>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>
> _______________________________________________
> Autoconf mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/autoconf
>