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From: daveb@rtech.UUCP (Dave Brower)
Newsgroups: comp.lang.c
Subject: Re: NULL pointers as arguments, really condition expressions
Message-ID: <801@rtech.UUCP>
Date: Mon, 4-May-87 00:08:24 EDT
Article-I.D.: rtech.801
Posted: Mon May  4 00:08:24 1987
Date-Received: Tue, 5-May-87 01:26:58 EDT
References: <1130@ius2.cs.cmu.edu> <148@nbisos.NBI.COM> <641@gargoyle.UChicago.EDU> <17780@sun.uucp>
Reply-To: daveb@rtech.UUCP (Dave Brower)
Distribution: na
Organization: Relational Technology, Alameda CA
Lines: 32

In article <17780@sun.uucp> guy%gorodish@Sun.COM (Guy Harris) writes:
>This means that if "cp" is of type "char *", then the expression
>
>	0 ? cp : 0
>
>has "the type of the pointer", namely "char *", while if "sxp" is of
>type "struct x *", the expression
>
>	0 ? sxp : 0
>
>has the type "struct x *".  Both expressions yield null pointers, and
>both expressions have different types.

Which reminds me of a general problem with the conditional operator.
What is the type of the result of evaluating:

	(expr) ? (double) x : (char)y

I believe it is undefined.   One could adopt a number of possible
rules for interpretation:

	* Take the type of the true expression as the type of the whole.
	* Take the type of the false expression...
	* Take the type of the lval, if any.
	* Take the type of the "biggest" type of the true or false expr.
	* Call it an error.

I'm inclined to call it an error.  Thoughts, anyone?

-dB
-- 
{amdahl, sun, mtxinu, cbosgd}!rtech!daveb daveb@rtech.uucp