C Macro question

[gaf at blu.org (Jerry Feldman)]

I write C code according to the C standard. vfprintf(3) is a standard 
function available on all standard C implementations. C preprocessor macros 
according to the standard do not support variable arguments. There are ways 
to get around this, but I dod not want to be overly complicated.
"Derek D. Martin" wrote:
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> At some point hitherto, Jerry Feldman hath spake thusly:
> > In short, macros do not support variable arguments, but....
> 
> Well, at least with Gnu tools, yes they do.  See my previous post.  I
> haven't tried this with any proprietary compiler, as I currently don't
> have access to any.
> 
> > You are better off using a C function for that (assume you include 
> > stdarg.h).
> > int printerr(const star *fmt, ...)
> > {
> > 	va_list ap;
> > 	int rv;
> > 	time_t now = time(NULL);
> > 	char msg[SOMESIZE];
> > 	va_start(ap, fmt);
> > 	sprintf(msg, "%s - ERROR: %s", ctime(&now), fmt);
> > 	rv = vfprintf(logfile, msg, ap);
> > 	return rv;
> > }
> 
> This reminds me; your implementation (if you're not using glibc) may
> not have vsnprintf().  If you're writing to a file, you can use a
> method something like gaf's above.  Most implementations have
> vfprintf() which make that possible.
> 
> If you're using some other API, such as to log a message to syslog,
> that won't work (because you need to have the message you're logging
> in a buffer to pass to syslog()).  In such a case, you can borrow the
> source for vsnprintf() from the glibc source.  Many Gnu programs
> explicitly include the source for functions added by the most recent C
> standards (such as vsnprintf()), as many older implementations don't
> have them.  Chances are fair that if you've got the source for any Gnu
> program laying around, the code for vsnprintf() might be with it.
> 
> - -- 
> Derek Martin               ddm at pizzashack.org    
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-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix user group
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