Using stderr in an initialization?

[Steve Kargl]

On Fri, May 02, 2008 at 01:43:55PM -0700, Bakul Shah wrote:
> On Fri, 02 May 2008 13:23:56 PDT Steve Kargl <sgk at troutmask.apl.washington.edu>  wrote:
> > I'm porting a piece of code to FreeBSD, and I've run into
> > a problem that I currently don't know how to solve. I scanned
> > both the Porter's Handbook and the Developer's Handbook, but
> > came up empty.
> > 
> > A reduce testcase is
> > 
> > #include <stdio.h>
> > 
> > typedef FILE *FILEP;
> > 
> > static FILEP outfile = {stderr};
> > 
> 	...
> > GCC gives
> > 
> > troutmask:sgk[204] cc -o z a.c
> > a.c:5: error: initializer element is not constant
> > a.c:5: error: (near initialization for 'outfile')
> > 
> >                                     So, anyone have a
> > suggestion on how to change line 5 to satisfy gcc?
> 
> It *used* to be the case that stderr was a macro referring to
> something like &_iob[2] which is a link time constant
> expression.  As per section 7.19.1 in the C standard, the
> stderr macro is an expression of type `pointer to file' but
> not a constant.  You wouldn't expect the following to work,
> would you?
> 
>     FILE* f;
>     FILE* outfile = f;
> 
> It is the exact same thing.  But you can do
> 
>     static FILE** _outfile = &stderr;
>     #define outfile (*_outfile)
> 
> to achive the effect you want.

Thanks for the suggestion.  This is K&R era code, and if
I read the dates in comments correctly, it predates the
formation of the ANSI C standard committee by more than
4 years.

-- 
Steve