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From: karl@haddock.UUCP (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: How big is a (??? *)
Message-ID: <564@haddock.UUCP>
Date: Mon, 15-Jun-87 17:48:27 EDT
Article-I.D.: haddock.564
Posted: Mon Jun 15 17:48:27 1987
Date-Received: Sun, 21-Jun-87 03:18:40 EDT
References: <737@edge.UUCP> <790@mcgill-vision.UUCP> <1243@epimass.EPI.COM> <353@formtek.UUCP> <1121@copper.TEK.COM>
Reply-To: karl@haddock.ISC.COM.UUCP (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 21

In article <1121@copper.TEK.COM> stevesu@copper.TEK.COM (Steve Summit) writes:
>>     "Nothing is said about pointers to functions, which may be
>>     incommensurate with object pointers and/or integers."  [dpANS:Rat]
>
>Why not?

One problem is efficiency, as you noted.  Why should normal programs, which do
not mix text/data pointers, have to pay the extra penalty to support esoteric
programs that do?

Also, on some machines (recall that the standard must address the least common
denominator, to some extent) there is nothing useful you can do with a
function pointer after casting it to a data pointer.  If the most that can be
done (in a portable program) is store it and get it back later, you might as
well use a union.

(Note that on machines in which it *is* safe and efficient, function-casting
will probably be implemented as an extension; this is acknowledged in dpANS
A.6.5.7 [Oct86])

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint