Re: Errors when including wchar.h, wctype.h and iostream

[Ian Lance Taylor <iant at google dot com>]

Yonatan Broza <shorttoedeagle@gmail.com> writes:

> Any idea on why the following code fails to compile?
>
> Changing the order of include directives or removing one of them solves the 
> problem.
>
> Is this a bug?
>
> Thanks!
>
> BEGIN_SESSION
> yb@chroot:~> cat include.cpp 
> #include <wchar.h>
> #include <wctype.h>
> #include <iostream>
>
> main() {}
> yb@chroot:~> g++ include.cpp 
> In file included from /usr/include/c++/4.3/cwchar:49,
>                  from /usr/include/c++/4.3/bits/postypes.h:47,
>                  from /usr/include/c++/4.3/iosfwd:47,
>                  from /usr/include/c++/4.3/ios:44,
>                  from /usr/include/c++/4.3/ostream:45,
>                  from /usr/include/c++/4.3/iostream:45,
>                  from include.cpp:3:
> /usr/include/c++/4.3/cstddef:55: error: â::ptrdiff_tâ has not been declared

This is a bug.  The bug appears to be in glibc.


/usr/include/wctype.h does this:

/* Get wint_t from <wchar.h>.  */
# define __need_wint_t
# include <wchar.h>


/usr/include/wchar.h does this:

#ifndef _WCHAR_H

#if !defined __need_mbstate_t && !defined __need_wint_t
# define _WCHAR_H 1
# include <features.h>
#endif

#ifdef _WCHAR_H

...

#endif	/* _WCHAR_H defined */

/* Undefined all __need_* constants in case we are included to get those
   constants but the whole file was already read.  */
#undef __need_mbstate_t
#undef __need_wint_t

#endif /* wchar.h  */


In other words, if you #include <wchar.h> before you #include
<wctype.h>, then _WCHAR_H is already defined, and <wchar.h> does not
#undef __need_wint_t.

The remaining #define of __need_wint_t remains to mess up the #include
of <stddef.h> which is done by <cstddef>.

The problem can be seen with a straight C file:

#include <wchar.h>
#include <wctype.h>
#include <stddef.h>
ptrdiff_t i;

I filed a glibc bug report:

http://sourceware.org/bugzilla/show_bug.cgi?id=9694

Thanks.

Ian