John W. Eaton wrote:
> I received a report about the following error on an OS X system:
>
> In file included from /usr/include/sys/time.h:197,
> from ../libgnu/sys/time.h:40,
> from ../libgnu/sys/select.h:51,
> from /usr/include/unistd.h:519,
> from ../libgnu/unistd.h:29,
> from
> /usr/include/c++/4.2.1/i686-apple-darwin10/bits/os_defines.h:61,
> from
> /usr/include/c++/4.2.1/i686-apple-darwin10/bits/c++config.h:41,
> from /usr/include/c++/4.2.1/cstddef:50,
> from Array.h:30,
> from MArray.h:28,
> from dMatrix.h:27,
> from ODESFunc.h:26,
> from ODES.h:26,
> from ODES.cc:27:
> ../libgnu/stdlib.h:737: error: previous declaration of ‘int
> _gl_warn_on_use’ with ‘C++’ linkage
> ../libgnu/time.h:350: error: conflicts with new declaration with ‘C’ linkage
>
> so it seems that _gl_warn_on_use should be declared extern "C" to
> avoid this kind of problem.
Yes, I agree. We cannot control whether all gnulib include files are included
in C++ mode. Here apparently <time.h> is included in C mode. This may be a
bug in the system include files; it may also lead to unintended consequences.
But anyway, it's safe to make the change you suggested. I've committed this:
2010-03-20 Bruno Haible <br...@clisp.org>
Make _GL_WARN_ON_USE usable in C++ and C mode in the same compilation.
* build-aux/warn-on-use.h (_GL_WARN_EXTERN_C): New macro.
(_GL_WARN_ON_USE, _GL_WARN_ON_USE_CXX): Likewise.
Reported by John W. Eaton <j...@gnu.org>.
--- build-aux/warn-on-use.h.orig Sun Mar 21 00:48:23 2010
+++ build-aux/warn-on-use.h Sun Mar 21 00:47:33 2010
@@ -70,7 +70,7 @@
# else /* Unsupported. */
# define _GL_WARN_ON_USE(function, message) \
-extern int _gl_warn_on_use
+_GL_WARN_EXTERN_C int _gl_warn_on_use
# endif
#endif
@@ -87,6 +87,16 @@
__attribute__ ((__warning__ (msg)))
# else /* Unsupported. */
# define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
-extern int _gl_warn_on_use
+_GL_WARN_EXTERN_C int _gl_warn_on_use
+# endif
+#endif
+
+/* _GL_WARN_EXTERN_C declaration;
+ performs the declaration with C linkage. */
+#ifndef _GL_WARN_EXTERN_C
+# if defined __cplusplus
+# define _GL_WARN_EXTERN_C extern "C"
+# else
+# define _GL_WARN_EXTERN_C extern
# endif
#endif
Additionally, it raises my attention to the fact that .h files must not have
#include statements inside extern "C" { ... } blocks. This fixes the two
violations of this rule that I can see in gnulib.
2010-03-20 Bruno Haible <br...@clisp.org>
Ensure no #include statements inside extern "C" { ... }.
* lib/obstack.h: Shrink extern "C" { ... } region so that it does not
contain #include statements.
* lib/time.in.h: Likewise.
--- lib/obstack.h.orig Sun Mar 21 01:12:15 2010
+++ lib/obstack.h Sun Mar 21 01:07:00 2010
@@ -103,10 +103,6 @@
#ifndef _OBSTACK_H
#define _OBSTACK_H 1
-
-#ifdef __cplusplus
-extern "C" {
-#endif
/* We need the type of a pointer subtraction. If __PTRDIFF_TYPE__ is
defined, as with GNU C, use that; that way we don't pollute the
@@ -139,6 +135,10 @@
#include <string.h>
+#ifdef __cplusplus
+extern "C" {
+#endif
+
struct _obstack_chunk /* Lives at front of each chunk. */
{
char *limit; /* 1 past end of this chunk */
--- lib/time.in.h.orig Sun Mar 21 01:12:15 2010
+++ lib/time.in.h Sun Mar 21 01:08:00 2010
@@ -46,10 +46,6 @@
/* The definition of _GL_WARN_ON_USE is copied here. */
-# ifdef __cplusplus
-extern "C" {
-# endif
-
/* Some systems don't define struct timespec (e.g., AIX 4.1, Ultrix 4.3).
Or they define it with the wrong member names or define it in <sys/time.h>
(e.g., FreeBSD circa 1997). */
@@ -57,6 +53,11 @@
# if @SYS_TIME_H_DEFINES_STRUCT_TIMESPEC@
# include <sys/time.h>
# else
+
+# ifdef __cplusplus
+extern "C" {
+# endif
+
# undef timespec
# define timespec rpl_timespec
struct timespec
@@ -64,11 +65,12 @@
time_t tv_sec;
long int tv_nsec;
};
-# endif
-# endif
-# ifdef __cplusplus
+# ifdef __cplusplus
}
+# endif
+
+# endif
# endif
/* Sleep for at least RQTP seconds unless interrupted, If interrupted,
