Path: utzoo!utgpu!watmath!iuvax!uxc.cso.uiuc.edu!tank!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: Variable number of arguments to functions
Keywords: how do i read a variable number of values?
Message-ID: <18233@mimsy.UUCP>
Date: 23 Jun 89 04:52:30 GMT
References: <22380@iuvax.cs.indiana.edu>
Distribution: na
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 57

In article <22380@iuvax.cs.indiana.edu> burleigh@silver.bacs.indiana.edu
(Frank Burleigh) writes:
>The vexing problem for me is that each pair of FILEA and FILEB
>files has a different number of values on the input lines.  I
>could compile different versions of the program to accommodate
>each pair, but that seems less than elegant.

Indeed.

>Apparently this is a problem to be solved by passing a variable
>number of arguments to vscanf() and vprintf() with the va_...
>macros in <stdarg.h>, but the procedures for this sort of
>application are not clear to me (from KR2 or Turbo C reference).

I do not know what led you to leap from `read a variable number of
values' to `supply a variable argument list to an I/O function'.  There
is a much simpler way to read a variable number of values, and that
is to make a variable number of read calls.  For instance:

	#include <stdlib.h>
	#include <stdio.h>
	#include <errno.h>
	#include <limits.h>
	#include <string.h>
	...
	long v;
	char *ptr, *eptr;
	FILE *stream;
	char buf[SIZE];
	...
	if (fgets(buf, sizeof(buf), stream) == NULL) {
		... handle EOF or error ...
	}
	ptr = buf;
	for (i = 0; i < values_per_line; i++) {
		ptr = strspn(ptr, " \t");	/* or whatever */
		if (ptr == NULL || *ptr == '#') {	/* # => comment */
			... handle ran-out-of-values ...
		}
		errno = 0;
		v = strtol(ptr, &eptr, 0);
		if ((v == LONG_MIN || v == LONG_MAX) && errno == ERANGE) {
			... handle value out of range ...
		}
		if (ptr == eptr) {
			... handle no digits ...
		}
	}
	if (ptr) {
		ptr = strspn(ptr, " \t");
		if (ptr && *ptr != '#') {
			... handle too much on line ...
		}
	}
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris