Re: [bug-gnulib] include in a C++ program

[Lorenzo Bettini]

Bruno Haible wrote:
> Lorenzo Bettini wrote:
> > I tried it and got no problem, but as far as I understand this is not a
> > proof, since
> >
> > #if defined HAVE_DECL_STRDUP && !HAVE_DECL_STRDUP && !defined strdup
> > /* Duplicate S, returning an identical malloc'd string.  */
> > extern char *strdup (const char *s);
> > #endif
> >
> > so the extern definition is not parsed, since it finds the definition of
> > strdup in string.h (included in strdup.h).
>
> Yes, the absence of a failure doesn't prove anything.
>
> > However, I tried this test program:
> >
> > #include <iostream>
> >
> > extern char *strdup (const char *s);
> >
> > int main()
> > {
> >   char *copy = strdup("foobar");
> >   std::cout << copy << std::endl;
> >
> >   return 0;
> > }
> >
> > and got no problem
>
> This doesn't prove anything either: <iostream> may include <string.h>, which
> may have an extern "C" declaration for strdup.
>
> Can you tell us the list of .h files that you want to use from C++? It's
> easier to make them C++ safe than to consider when exactly the extern "C"
> will be needed or not.

You're right: iostream somehow includes string.h: if I remove such 
include then I get the linkage error with this program (I forced in 
strdup.c the use of the version not in string.h)

extern char *strdup (const char *s);

int main()
{
  char *copy = strdup("foobar");

  return (copy != 0 ? 0 : 1);
}

I thus included a possible patch.

thanks
        Lorenzo

--
+-----------------------------------------------------+
| Lorenzo Bettini          ICQ# lbetto, 16080134      |
| PhD in Computer Science, DSI, Univ. di Firenze      |
| Florence - Italy        (GNU/Linux User # 158233)   |
| http://www.lorenzobettini.it                        |
| http://tronprog.blogspot.com  BLOG                  |
| http://www.purplesucker.com Deep Purple Cover Band  |
| http://www.gnu.org/software/src-highlite            |
| http://www.gnu.org/software/gengetopt               |
| http://www.gnu.org/software/gengen                  |
| http://doublecpp.sourceforge.net                    |
+-----------------------------------------------------+

Index: lib/strdup.h
===================================================================
RCS file: /sources/gnulib/gnulib/lib/strdup.h,v
retrieving revision 1.3
diff -U3 -r1.3 strdup.h
--- lib/strdup.h        14 May 2005 06:03:58 -0000      1.3
+++ lib/strdup.h        19 Dec 2006 14:49:15 -0000
@@ -22,8 +22,18 @@
 #include <string.h>
 
 #if defined HAVE_DECL_STRDUP && !HAVE_DECL_STRDUP && !defined strdup
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
 /* Duplicate S, returning an identical malloc'd string.  */
 extern char *strdup (const char *s);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
 #endif
 
 #endif /* STRDUP_H_ */