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From: bron@bronze.wpd.sgi.com (Bron Campbell Nelson)
Newsgroups: comp.sys.sgi
Subject: Re: comparing pointers to void functions
Summary: void and void* in 3.2 have problems
Message-ID: <61182@sgi.sgi.com>
Date: 30 May 90 06:37:05 GMT
References: <9454@pt.cs.cmu.edu> <61180@sgi.sgi.com>
Sender: bron@bronze.wpd.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 31

In article <61180@sgi.sgi.com>, rpw3@rigden.wpd.sgi.com (Rob Warnock) writes:
> In article <9454@pt.cs.cmu.edu> cycy@isl1.ri.cmu.edu (Scum) writes:
[edited to reduced bandwidth]
> +---------------
> | ...                                     I'm having a problem trying to
> | determine if a pointer is pointing to a certain function. The pointer is
> | defined as an element in a structure thusly:
> | 	struct object {
> | 		void (*formstart) ();
> | 	}
> | However, the compiler will not accept the following attempt to compare the
> | pointer to the address of the function, even though when they are printed
> | out, their values are the same:
> | 		if (thing->formstart == bgnpolygon)
> +---------------
> ... on the 3.2 C compiler that still gives the error you saw.
> 
> On a 3.3 (to be released) compiler, neither version of either form gives
> an error (and the generated code looks correct). So I guess it's "fixed
> in some to-be-determined release"...

The short answer is that the compilers used in the SGI 3.2 release
had various sorts of problems with void and void* types.  This is one
of them.  As Rob says, these problems are fixed in the 3.3 version, due
out Real Soon Now.   Casting the types to char*() to do the compare is a
bit ugly, but I think it should work until 3.3 is available.

--
Bron Campbell Nelson
bron@sgi.com  or possibly  ..!ames!sgi!bron
These statements are my own, not those of Silicon Graphics.