C Macro question

[fjr at marsdome.myip.org]

Jerry,
    thanks for the code snipet.  That provided exactly what I needed
 :)

                 -fjr

----Original Message-----
   >From:     	Jerry Feldman <gaf at blu.org>
   >To:         	discuss at blu.org
   >Subj:     	Re: C Macro question 
   >Sent:    	Sunday, June 16, 2002 6:11 PM
   >
   >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:
   >> -----BEGIN PGP SIGNED MESSAGE-----
   >> Hash: SHA1
   >> 
   >> 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
   >http://www.blu.org PGP key id:C5061EA9
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