Path: utzoo!attcan!uunet!munnari.oz.au!goanna!ok
From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.lang.c
Subject: Re: Why use (void) func() ?
Message-ID: <3819@goanna.cs.rmit.oz.au>
Date: 25 Sep 90 04:10:22 GMT
References: <586@dptechno.UUCP>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 64

In article <586@dptechno.UUCP>, dave@dptechno.uucp (Dave Lee)
[claims that he never accidentally omits to check the result of a
 function, and asks why lint complains about it.  He specifically
 cites printf().]

> Why should I go to the extra trouble to write
> 	(void) printf("hello world\n");
> Instead of 
> 	printf("hello world\n");

Stop and think for a moment.  Why might lint have been made to check
for this in the first place?  The answer is simple:  the result that
you are ignoring is the only error indication you are going to get,
and ignoring it _may_ be very silly.  I am sick of UNIX programs whose
authors KNEW that they could safely ignore the result of (say) write(),
with the result that I have lost valuable files because write errors
were ignored.  (It's no good relying on a source management system to
protect your old versions when the source management system itself is
capable of storing large blocks of 0s for this very reason.)

printf() used to return 0 for success, -ve for failure.
In ANSI C, printf() returns #characters written for success, -ve for
failure.  Are you _sure_ that you know all the causes of error in a
call to printf() -- such as output being written to a file on a disc
that has just filled up -- and have ensured that they can't happen?

You might like to use something like

#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>

static void error(void)		/* BEWARE: This is UNIX-specific */
    {				/* if you've closed stderr, we're sunk */
	static char message[] = "Error in ?printf\n";
	write(2, message, sizeof message - 1);
	exit(EXIT_FAILURE);
    }

void eprintf(char *format, ...)
    {
	va_list ap;
	int t;

	va_start(ap, format);
	t = vprintf(format, ap)
	va_end(ap);
	if (t < 0) error();
    }

void efprintf(FILE *stream, char *format, ...)
    {
	va_list ap;
	int t;

	va_start(ap, format);
	t = vfprintf(stream, format, ap)
	va_end(ap);
	if (t < 0) error();
    }

/* end of file */
-- 
Heuer's Law:  Any feature is a bug unless it can be turned off.