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From: joe@fluke.UUCP (Joe Kelsey)
Newsgroups: net.bugs.4bsd
Subject: bug in putc macro in <stdio.h>
Message-ID: <1747@vax4.fluke.UUCP>
Date: Thu, 26-Jul-84 18:07:42 EDT
Article-I.D.: vax4.1747
Posted: Thu Jul 26 18:07:42 1984
Date-Received: Sat, 28-Jul-84 09:17:25 EDT
Organization: John Fluke Mfg. Co., Everett, WA
Lines: 36

Index:	/usr/include/stdio.h ALL UNIX SYSTEMS!!!

Description:
	Remember all of the flack recently about sign extension and
	getc?  Whether or not you can compare (c = getc(stdin)) == EOF?
	Well, how about the same discussion related to putc?  Yes, there
	are programmers who check the value returned by putc.  The main
	problem is to detect errors indicated by _flsbuf, as in quota
	exceeded, or other disastrous errors.  However, putc(0xff, stdout)
	gets sign extended (on DEC hardware, anyway) so that you can't
	tell it from EOF (-1).
Repeat-By:
	#include <stdio.h>
	
	main()
	{
		int x;
		
		if ((x = putc(0xff, stdout)) == EOF) {
			printf (stderr, "Error!\n");
		} else {
			printf (stderr, "OK!\n);
		}
	}
Fix:
	Add a mask to the putc macro in <stdio.h>.  Note that I have verified
	this bug in VAX-11 C also!
old:
#define putc(x,p) (--(p)->_cnt>=0? ((int)(*(p)->_ptr++=(unsigned)(x))):_flsbuf((unsigned)(x),p))
new:
#define putc(x,p) (--(p)->_cnt>=0? ((int)(*(p)->_ptr++=(unsigned)(x)))&0xff:_flsbuf((unsigned)(x),p))

	This change merely makes putc operate the same as getc when filling
	the buffer before actually attempting to output the buffer.

/Joe