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From: mnc@m10ux.UUCP
Newsgroups: comp.lang.c,comp.unix.wizards
Subject: C Compiler Bug (possibly widespread)
Message-ID: <203@m10ux.UUCP>
Date: Mon, 27-Apr-87 15:56:49 EDT
Article-I.D.: m10ux.203
Posted: Mon Apr 27 15:56:49 1987
Date-Received: Sat, 2-May-87 01:47:23 EDT
Organization: AT&T Bell Labs, Murray Hill
Lines: 23
Keywords: SystemV Sun C Compilers
Xref: utgpu comp.lang.c:1919 comp.unix.wizards:1943

Here is a nasty little bug I just ran into with the Sys V R2 (VAX) C
compiler and the Sun C compiler (but it does not exist on 4.3 BSD).
Consider:

	extern void f(), (*fp)();
	int x;
	main() {
		g(x ? f :  fp);
		g(x ? f : *fp);
	}

Both of the uses of the "? :" operator produce the message "operands of
: have incompatible types".  Changing "void" to any other type makes
both error messages go away.  Notice that there is no attempt to use
a void value in the above expression.  Since this code is likely to
occur in any C program that passes procedures (i.e. void functions) as
arguments, I don't understand how the bug could have persisted this long.
The only work-around I can think of (besides changing the declaration of
f and fp) is to use "if - else" instead of "? - :".
-- 
Michael Condict		{ihnp4|vax135|cuae2}!m10ux!mnc
AT&T Bell Labs		(201)582-5911    MH 3B-416
Murray Hill, NJ