Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!samsung!rex!ames!excelan!crdgw1!sixhub!davidsen
From: davidsen@sixhub.UUCP (Wm E. Davidsen Jr)
Newsgroups: comp.lang.c
Subject: Re: Typeof operator in C (Re: An Interesting View of "Strong" Vs. "Weak" Typing)
Message-ID: <405@sixhub.UUCP>
Date: 16 Jan 90 01:48:51 GMT
References: <16678@megaron.cs.arizona.edu> <7106@tank.uchicago.edu> <-K016ODxds13@ficc.uu.net> <5263@buengc.BU.EDU>
Reply-To: davidsen@sixhub.UUCP (bill davidsen)
Organization: *IX Public Access UNIX, Schenectady NY
Lines: 29

In article <5263@buengc.BU.EDU> bph@buengc.bu.edu (Blair P. Houghton) writes:

| >But a typeof operator... wouldn't that be something...
| >
| >#define SWAP(a,b) {typeof a tmp; tmp=a; a=b; b=tmp}
| 
| Oboy.  Saved a few char's in the source code...

  That's not what it's for. You have avoided a possible error caused by
changing the type of the items to be swapped. By forcing the temp to be
the same type as the items you avoid a type conversion, which could be
(a) slow and (b) might generate a roundoff or data loss error.

  Now my question (no gcc docs on this machine) is, does this return a
numeric value? In other words, can I improve my error checking in the
macro by saying something like:
	#define SWAP(a,b) {typeof a tmp;\
	assert(typeof a == typeof b);\
	tmp = a; a = b; b = tmp; }

  All this requires is that the evaluation return a discrete value for
all types, but the user defined types would be a problem. I can envision
a PRINT macro which would use typeof to select the format of the print.
I can envision it, and it's UGLY...
-- 
	bill davidsen - sysop *IX BBS and Public Access UNIX
davidsen@sixhub.uucp		...!uunet!crdgw1!sixhub!davidsen

"Getting old is bad, but it beats the hell out of the alternative" -anon