Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!lll-winken!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.lang.c
Subject: Re: The Dangers of sizeof
Keywords: sizeof
Message-ID: <1416@auspex.auspex.com>
Date: 10 Apr 89 19:20:40 GMT
References: <9969@smoke.BRL.MIL> <3.UUL1.3#5109@pantor.UUCP> <105@servio.UUCP>
Reply-To: guy@auspex.auspex.com (Guy Harris)
Organization: Auspex Systems, Santa Clara
Lines: 41


 >I must disagree!

So must I, but that's because I know for a fact that you're wrong.

 >There is only ONE form of sizeof -- the operator form,
 >which takes an arbitrary (unevaluated) expression as its argument.

Wrong.  "sizeof" is, indeed, an operator in both forms; however, the
notion that

 >sizeof (aType) is actually the same as
 >
 >sizeof (aType)(1)
 >
 >(i.e, casting the empty expression).

is not backed up by any language specification I've seen.  K&R I has two
separate grammar rules for the two forms; the December 7, 1988 (d)pANS
says that

	...The 'sizeof' operator yields the size (n bytes) of its
	operand, which may be an expression or the parenthesized name of
	a type.

 >Trick question:  what is the value of:
 >
 >sizeof (char) - 1
 >
 >Answer:  1 -- the (char) is a cast, which is of higher precedence than
 >sizeof, hence it parses as,
 >
 >sizeof ((char)(- 1))

Yeah, that must *be* a trick question, considering you got it wrong. 
The answer is 0, not 1; the "(char)" is *NOT* a cast, it's part of the
"sizeof" expression, so it parses as

	(sizeof (char)) - 1

Are you sure you didn't mean to post this on April 1?