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From: whp@cbnap.UUCP (W. H. Pollock x4575 3S235)
Newsgroups: net.lang.c,net.bugs
Subject: Re: C Compiler bug (?: operator)
Message-ID: <155@cbnap.UUCP>
Date: Thu, 31-Jul-86 09:12:59 EDT
Article-I.D.: cbnap.155
Posted: Thu Jul 31 09:12:59 1986
Date-Received: Sat, 2-Aug-86 03:33:30 EDT
References: <273@watmath.UUCP> <5858@alice.uUCp> <134@sas.UUCP>
Reply-To: whp@cbnap.UUCP (W. H. Pollock x4575 3S235)
Organization: AT&T Bell Laboratories, Columbus
Lines: 40
Xref: watmath net.lang.c:10115 net.bugs:853
Summary: conditional operator semantics (?:)

In article <134@sas.UUCP> jcz@sas.UUCP (Carl Zeigler) writes:
>
>  > > void f3(which)
>  > > {
>  > >     extern void f1(),f2();
>  > >     which?f1():f2();
>  > > }
>  > > cc(1) gives an "incompatible types" error.
>  > 
>  > As it should.  The only thing you're allowed to do with void values
>  > is throw them away.
>
>Scan again, Andrew, the (void) values are being thrown away.

The void values are not thrown away!  Remember that (A?B:C) is an
expression *returning a value*.  C is giving the error because it can't
determine the type of the return value.  This is clearer in the following:

	void f3(which)
	{
	    int f1();
	    void f2();
	    int foo;
	    ...
	    foo = which?f1():f2();
	    ...
	}

which results in the same error message, for the same reason.  Another
example:

	f4()
	{
	    ...
	    return ((void) expression);
	}

Note it doesn't mater what use is made of the return value (in the original
example it is thrown on the floor, which is what probably confused some
people).