Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!utcsri!greg
From: greg@utcsri.UUCP
Newsgroups: comp.lang.c
Subject: Re: typeof(), like sizeof() (Was: Question on structures)
Message-ID: <5667@utcsri.UUCP>
Date: Sun, 15-Nov-87 20:33:33 EST
Article-I.D.: utcsri.5667
Posted: Sun Nov 15 20:33:33 1987
Date-Received: Tue, 17-Nov-87 02:57:28 EST
References: <1025@phoenix.Princeton.EDU> <3022@bunker.UUCP> <150@fxgrp.UUCP> <3025@bobkat.UUCP> <1827@chinet.UUCP>
Reply-To: greg@utcsri.UUCP (Gregory Smith)
Organization: CSRI, University of Toronto
Lines: 49
Keywords: life, macros, and everything and the inverse thereof.
Summary: 

In article <1827@chinet.UUCP> dag@chinet.UUCP (Daniel A. Glasser) writes:
>Though the typeof(thing) facility which is being described in the above
>article might be nice, it could not be a part of the preprocessor pass.

True.

>So the typeof operator (if you don't already know, sizeof is an operator
>and only requires the "()"s for grouping.) would be a language extension,
>not a preprocessor extension.  This operator might be useful, but does not
>fit anywhere in the current language definition.  The semantics would
>have to be similar to declaration of identifiers, but in
>
>	int foo;
>
>"int" is not an operator.  Maybe it could be restricted to typecast
>semantics, but this would reduce its usefulness.
>
How about this:

*type-specifier*:
	char
	short
	...
	typeof ( *expression* )	<< add this ( parens probably essential
				   for parsibility )
	typeof ( *type-name* )  << and this

*type-name*:		<< one of many productions missing from K&R
	*type-specifier* *abstract-declarator*

(type-name is anything you can put in parens to get a cast, or give to
sizeof as a type).
I would say it fits in pretty cleanly.
The second case "typeof( *type-name* )" seems a little redundant,
but it allows this:
	typeof( int *(*)()) x,y,z;
instead of
	int *(*x)(), *(*y)(), *(*z)();
or
	typedef int *(*pfpi)();
	pfpi x,y,z;
Which might be very handy for certain preprocessers producing C output.

#define new(ptr)  ((ptr) = (typeof (ptr))malloc( sizeof( *(ptr) )))

-- 
----------------------------------------------------------------------
Greg Smith     University of Toronto      UUCP: ..utzoo!utcsri!greg
Have vAX, will hack...