Re: fixincludes of C++ friendly NULLs

[Mike Stump <mrs at apple dot com>]

On Oct 27, 2004, at 2:34 AM, Nathan Sidwell wrote:

> Mike Stump wrote:
>
> > This patch fixes the fixincluding of C++ friendly NULLs...
>
>
> > +     /* avoid changing C++ friendly NULL */
> > +     bypass    = __cplusplus;
> >       select    = "^#[ \t]*define[ \t]+NULL[ \t]+\\(\\(void[ 
> > \t]*\\*\\)0\\)";
> >       c_fix     = format;
> >       c_fix_arg = "#define NULL 0";
>
> I don't understand, isn't this fix changing a C++ unfriendly NULL
> to a C++ friendly one?  What is the bug being fixed?

The standard definition of NULL is (from stdlib.h):

#ifndef NULL
#ifdef __GNUG__
#define NULL __null
#else /* ! __GNUG__ */
#ifndef __cplusplus
#define NULL ((void *)0)
#else /* __cplusplus */
#define NULL 0
#endif /* ! __cplusplus */
#endif /* __GNUG__ */
#endif /* ! NULL */

On some systems, they've _fixed_ their header files to be C++ safe.  
The above, if a good definition for a C++ safe version of NULL.  The 
problem will fixincludes, is that it _fixes_ the above correct code, to 
be incorrect:

#ifndef NULL
#ifdef __GNUG__
#define NULL __null
#else /* ! __GNUG__ */
#ifndef __cplusplus
#define NULL 0
#else /* __cplusplus */
#define NULL 0
#endif /* ! __cplusplus */
#endif /* __GNUG__ */
#endif /* ! NULL */

This is wrong.  By avoiding fixing any file that is C++ safe, we 
preserve the goodness of the original file.  If there is no C++ 
goodness in the file, only thjen do we allow it to clobber things.