Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!asuvax!noao!ncar!midway!uwvax!sevenlayer.cs.wisc.edu!bothner
From: bothner@sevenlayer.cs.wisc.edu (Per Bothner)
Newsgroups: comp.lang.c++
Subject: Re: Pointer arithmetic
Keywords: char* vs void* pointer arithmitic
Message-ID: <1991Jan4.211448.27626@spool.cs.wisc.edu>
Date: 4 Jan 91 21:14:48 GMT
References: <1991Jan4.191051.3995@demott.com>
Sender: news@spool.cs.wisc.edu (The News)
Organization: U of Wisconsin CS Dept
Lines: 22

In article <1991Jan4.191051.3995@demott.com> kdq@demott.COM (Kevin D. Quitt) writes:
>
>    What about the subtraction of pointers to get a constant?  I discovered
>that gcc does not allow:
>	int = strchr( string, char ) - &string;
>to determine the position of char within string.  Is there a (good) reason
>for disallowing this?

Perhaps because it's wrong? It should be:
	int i = strchr( str, ch ) - str;
(Note: no '&' before the string.)

Also, you need a prototype for strchr, so that the compiler can
know that the return type is (char*) and not (int).
libg++ has such a prototype in <std.h>.

Once you make these fixes, I'm sure gcc/g++ will allow your example.


-- 
	--Per Bothner
bothner@cs.wisc.edu Computer Sciences Dept, U. of Wisconsin-Madison