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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: using varargs function to call another varargs function
Message-ID: <7269@mimsy.UUCP>
Date: Tue, 30-Jun-87 21:16:53 EDT
Article-I.D.: mimsy.7269
Posted: Tue Jun 30 21:16:53 1987
Date-Received: Wed, 1-Jul-87 07:24:27 EDT
References: <1332@rosevax.Rosemount.COM> <7268@mimsy.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 55

Oops:  I left a `va_end(l)' out of the source in the parent article,
<7268@mimsy.UUCP>.  For a second example, here is the error()
routine from the local C library.  Note that it `cheats' by declaring
three fixed arguments before the variable argument list.  It also
depends on crt0.o (the thing that calls main()) to set `_argv0'
equal to main's argv[0].  This way all programs that call `error'
print out their own names before printing their error messages.

#include <stdio.h>
#include <varargs.h>

char *_argv0;			/* argv[0], set by C startup code */

/*
 * error - University of Maryland specific (sigh)
 *
 * Useful for printing error messages.  Will print the program name
 * and (optionally) the system error associated with the values in
 * <errno.h>.
 */
error(quit, e, fmt, va_alist)
	int quit;
	register int e;
	char *fmt;
	va_dcl
{
	extern char *sys_errlist[];
	extern int sys_nerr, errno;
	va_list l;
	register char *p = _argv0;

	if (e < 0)
		e = errno;
	(void) fflush(stdout);		/* somewhat gratuitous */
	if (p != NULL)
		(void) fprintf(stderr, "%s: ", p);
/*** the next three lines are the interesting ones ***/
	va_start(l);
	(void) vfprintf(stderr, fmt, l);
	va_end(l);
/******/
	if (e > 0) {
		if (e < sys_nerr)
			(void) fprintf(stderr, ": %s", sys_errlist[e]);
		else
			(void) fprintf(stderr, ": unknown error number %d", e);
	}
	(void) putc('\n', stderr);
	(void) fflush(stderr);
	if (quit)
		exit(quit);
}
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	seismo!mimsy!chris