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# ===========================================================================
# https://www.gnu.org/software/autoconf-archive/ax_cc_tentdef.html
# ===========================================================================
#
# SYNOPSIS
#
# AX_CC_TENTDEF
#
# DESCRIPTION
#
# Determine whether the C compiler supports C tentative definitions. See
# K&R book Appendix A10.2 on 'extern' and tentative definitions. Some
# compilers use a 'strict definition-reference model' Traditionally most
# UNIX C compilers support tentative definitions, whereas some compiler
# such as Metrowerks or WATCOM C do not.
#
# The $ac_cv_tentdef variable will be either no or yes, and can be
# overridden on the command line using --with-tentdef
#
# See also: ax_cc_attrcommon.m4 for a __attribute__(( __common__)) test
#
# LICENSE
#
# Copyright (c) 1996-2023 David Stes
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation, either version 3 of the License, or (at your
# option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
# Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program. If not, see <https://www.gnu.org/licenses/>.
#serial 4
AC_ARG_WITH(tentdef,
[ --with-tentdef use C tentative definitions],
[ac_cv_tentdef=$withval]
)
AC_DEFUN([AX_CC_TENTDEF],
[
AC_MSG_CHECKING(whether compiler supports C tentative definitions)
AC_CACHE_VAL(ac_cv_tentdef,[
t1="x$$.c"
t2="y$$.c"
e1="x$$"
e2="y$$"
ac_clean_files="$e1 $e2 $t1 $t2"
# this is the traditional case for most compilers (K&R book Appendix A10.2)
# tentative definitions are resolved using 'common storage'
# this case is supported by setting CC to 'gcc -fcommon'
# which is since gcc 10 not the default (it defaults now to -fno-common)
cat >$t1 <<EOF
int a = 7;
EOF
cat >$t2 <<EOF
#include <stdio.h>
int a;
int main() { exit(a);return a; }
EOF
echo "$CC $t1 $t2 -o $e1" >&5
($CC $t1 $t2 -o $e1) 2>&5 1>&5
echo "$CC $t2 $t1 -o $e2" >&5
($CC $t2 $t1 -o $e2) 2>&5 1>&5
if test -x ./$e1 -a -x ./$e2
then
echo -n "check whether $e1 returns '7'" >&5
if ./$e1 != 7
then
echo " (no)" >&5
ac_cv_tentdef=no;
else
echo " (yes)" >&5
echo -n "check whether $e2 returns '7'" >&5
if ./$e2 != 7
then
echo " (no)" >&5
ac_cv_tentdef=no
else
echo " (yes)" >&5
ac_cv_tentdef=yes;
fi
fi
else
ac_cv_tentdef=no;
fi
rm -rf $ac_clean_files
],ac_cv_tentdef=no,ac_cv_tentdef=yes)
AC_MSG_RESULT($ac_cv_tentdef)
])
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