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From: ado@elsie.UUCP (Arthur David Olson)
Newsgroups: net.bugs.4bsd
Subject: 4.[12]bsd putc's "return value" is inconsistent (with fix and caution)
Message-ID: <6033@elsie.UUCP>
Date: Tue, 25-Feb-86 19:59:25 EST
Article-I.D.: elsie.6033
Posted: Tue Feb 25 19:59:25 1986
Date-Received: Fri, 28-Feb-86 06:33:20 EST
Organization: NIH-LEC, Bethesda, MD
Lines: 49
Keywords: bsd putc

Index:	include/stdio.h

Description:
	The putc macro may "return" different values when asked to output
	the same value.

Repeat-By:
	Compiling this code:

		#include "stdio.h"

		main()
		{
			int	a, b;

			a = putc(128 + '\n', stdout);
			b = putc(128 + '\n', stdout);
			printf("a: %d\n", a);
			printf("b: %d\n", b);
		}

	then running the resulting executable, piping its output to "od -c"
	and noting the results:

	0000000 212 212   a   :       1   3   8  \n   b   :       -   1   1   8
	0000020  \n  \0
	0000021

Fix:
	Since the "fputc" function returns 138 in both cases, the thing to
	do seems to be to change the "putc" macro to do so as well.  Here's
	the change for the 4.1bsd version of "stdio.h", conditioned on
	"OLDVERSION":

#ifdef OLDVERSION
#define putc(x,p) (--(p)->_cnt>=0? ((int)(*(p)->_ptr++=(unsigned)(x))):_flsbuf((unsigned)(x),p))
#else
#define putc(x,p) (--(p)->_cnt>=0? ((int)((unsigned char)(*(p)->_ptr++=(x)))):_flsbuf((unsigned)(x),p))
#endif

	Folks intersted in producing portable code will want to be aware of
	the above bug and take pains to walk around it (for example, calling
	ferror rather than checking putc's "return value" when all that's
	being done is error checking).
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