AC_C_RESTRICT and C/C++

[Bruno Haible]

Hi Paul,

Got this gettext testsuite failure with Sun C/C++ 5.0 on Solaris 10:

  "../gnulib-lib/string.h", line 109: Error: ")" expected instead of "__dst".
  "../gnulib-lib/string.h", line 124: Error: ")" expected instead of "__dst".
  2 Error(s) detected.
  FAIL: lang-c++

What's happening? gnulib's string.h replacement uses the 'restrict' keyword.
AC_C_RESTRICT has put this into config.h:

  #define restrict _Restrict

The lang-c++ test has this C++ code:

  #include "config.h"
  ...
  indirectly #include <string.h>

But the definition of 'restrict' is not valid for the C++ compiler.

$ which cc
/opt/SUNWspro/SC5.0/bin/cc
$ which CC
/opt/SUNWspro/SC5.0/bin/CC
$ cat foo.c
#define restrict _Restrict
extern char *stpcpy (char *restrict __dst, char const *restrict __src);
$ cc -c foo.c; echo $?
0
$ ln foo.c foo.cc
$ CC -c foo.cc; echo $?
"foo.cc", line 2: Error: ")" expected instead of "__dst".
1 Error(s) detected.
1

This report is similar to the one for gcc / g++ in [1]. It was said in [2]
that "`restrict' is not yet a standard C++ feature."

IMO the issue would be solved if autoconf's AC_C_RESTRICT macro was changed
to emit into config.h a code like this:

  /* Define to equivalent of C99 restrict keyword, or to nothing if this
     is not supported.  Do not define if restrict is supported directly.  */
  #ifdef __cplusplus
  #define restrict
  #else
  #define restrict _Restrict
  #endif

I cannot propose a patch, since I don't know how to mix AC_DEFINE and
AC_VERBATIM appropriately.

Bruno


[1] http://lists.gnu.org/archive/html/bug-autoconf/2007-05/msg00013.html
[2] http://lists.gnu.org/archive/html/bug-autoconf/2007-05/msg00016.html