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From: hymie@dvm.UUCP (Hyman Rosen)
Newsgroups: comp.lang.c
Subject: Re: Object oriented programming in C
Message-ID: <113@dvm.UUCP>
Date: Fri, 21-Nov-86 03:51:23 EST
Article-I.D.: dvm.113
Posted: Fri Nov 21 03:51:23 1986
Date-Received: Fri, 21-Nov-86 20:14:10 EST
References: <1497@batcomputer.tn.cornell.edu>
Reply-To: hymie@dvm.UUCP (Hyman Rosen)
Distribution: world
Organization: Philon, Inc. (NY, NY)
Lines: 50

In article <1497@batcomputer.tn.cornell.edu> braner@batcomputer.UUCP (braner) writes:
>[]
>
>A while ago I posted a method to do object oriented programming in C.
>At the heart of the method is a function that is called every time a
>method is being looked up.  This function, called FindMethod, returns
>the address of the method - a pointer to a function.  Now how do you declare
>a function of that type?  A variable of type pointer to a function which
>in turn returns an int is declared as:
>
>	int (*foo)();
>
>and in my posting I declared FindMethod as:
>
>	int (*FindMethod())(token,obp);
>
>Turns out that the correct syntax is:
>
>	int (*FindMethod(token,obp))();
>
>What is surprising is that the compiler I used (Megamax C on the Atari ST)
>did not complain, and went on to produce code that did just what I intended!
>But other compilers complained.  Thanks to Don Howes that notified me of the
>problem.
>
>- Moshe Braner

	First of all, you ought to consider using typedef to simplify
declarations like that, but that does take all the joy out of life,
doesn't it? :-) In any how, there is a reason why some compilers accept
the incorrect syntax. It's because of one of the very few bugs in K&R.
The C reference manual in the back says that

	function-declarator:	declarator ( parameter-list-opt )

which is the syntax you tried using. Nevertheless, it is incorrect, and
now most compilers accept only the proper syntax.

	Remember that the intent of C declarations is to mimic the use of
the variable being declared. When you actually call FindMethod, you use
FindMethod(token,obp). You do *not* pass those arguments to the function
whose pointer is returned by FindMethod. When defining a function in C,
the arguments always go in the set of parentheses immediately following
the name of the function.
-- 


								- Hymie

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