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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.lang.c
Subject: Re: NULL pointers as arguments, really condition expressions
Message-ID: <17965@sun.uucp>
Date: Mon, 4-May-87 14:19:27 EDT
Article-I.D.: sun.17965
Posted: Mon May  4 14:19:27 1987
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> What is the type of the result of evaluating:
> 
> 	(expr) ? (double) x : (char)y
> 
> I believe it is undefined.

Well, you're wrong.

> 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?

"Take the type of the 'biggest' type of the true or false expr" comes
closest to the specified rules.  From K&R:

	7.13 Conditional operator

	...If possible, the usual arithmetic conversions are
	performed to bring the second and third expressions to a
	common type; otherwise, if both are pointers of the same
	type, the result has the common type; otherwise, one must be
	a pointer and the other the constant 0, and the result has
	the type of the pointer.

and from the October 1, 1986 ANSI C draft:

	3.3.15 Conditional operator

	...

	   The first operand shall have scalar type.  Both the second
	and third operands may have arithmetic type, or may have the
	same structure, union, or pointer type, or may be void
	expressions.  In addition, one may be a pointer and the other
	a null pointer constant, or one may be a pointer to an object
	and the other a pointer to 'void'.

	...

	   If both the second and third operands have arithmetic type,
	the usual arithmetic conversions are performed to bring them
	to the same type, and the result has that type.  If both the
	operands have structure, union, or pointer type, the result
	has that type.  If both the operands are void expressions,
	the result is a void expression.  If one of the operands is a
	pointer to an object and the other is a pointer to 'void',
	the pointer to an object is converted to type pointer to
	'void', and the result has that type.  If one operand is a
	pointer and the other operand a null pointer constant, the
	result has the type of the pointer.