Hi,
The NEWS of autoconf 2.60 has this:
** AC_PROG_CC_STDC
Has been unobsoleted, and will check if the compiler supports ISO
C99, falling back to ANSI C89 if not.
This leads to a problem: AC_C_RESTRICT, AC_PROG_CC_STDC, and mixed C/C++
are incompatible.
In detail:
My package consists of mixed C and C++ source code. It uses a single config.h
for both parts (please don't recommend two different config.h's, one for C and
one for C++ - that would be an unacceptable complexity).
The package uses 'restrict' like this:
extern char *stpcpy (char *restrict dst, char const *restrict src);
and therefore invokes AC_C_RESTRICT.
The package also uses the gnulib module 'stdarg', which contains the following
code:
dnl Some compilers (e.g., AIX 5.3 cc) need to be in c99 mode
dnl for the builtin va_copy to work. With Autoconf 2.60 or later,
dnl AC_PROG_CC_STDC arranges for this. With older Autoconf AC_PROG_CC_STDC
dnl shouldn't hurt, though installers are on their own to set c99 mode.
AC_REQUIRE([AC_PROG_CC_STDC])
I try to compile it on mingw, where the C compiler is gcc version 3.4.2 and
the C++ compiler is g++ version 3.4.2.
At configuration time, 'configure' runs AC_PROG_CC_STDC first, then
AC_C_RESTRICT. During the AC_PROG_CC_STDC run, it changes the CC variable
from "gcc" to "gcc -std=gnu99". The AC_C_RESTRICT test is run with this
compiler, detecting that the C compiler supports 'restrict'. config.h then
contains this:
/* #undef restrict */
At "make" time, the compilation of the C++ parts of the package fails with
a syntax error.
The support of 'restrict' and '__restrict' is this:
| restrict | __restrict
----------------+--------------+---------------
gcc | no | yes
gcc -std=gnu99 | yes | yes
g++ | no | yes
Should I work around this in my package? I'd say no, because the use of
AC_C_RESTRICT, AC_PROG_CC_STDC, and C++ are widespread elsewhere as well.
Should my package not invoke AC_PROG_CC_STDC? I'd say no, because the C99
mode is needed for AIX and stdarg.
Should my package not invoke AC_C_RESTRICT? Well. What other macro does
autoconf provide that defines 'restrict' appropriately?
The minimally invasive change is probably that AC_C_RESTRICT defines
'restrict' to '__restrict', if the compiler is gcc >= 2.95, even if
the C compiler also supports 'restrict' natively.
Bruno
