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From: guy@sun.uucp (Guy Harris)
Newsgroups: comp.lang.c
Subject: Re: how do I initialize a function pointer to be NULL ?
Message-ID: <27742@sun.uucp>
Date: Fri, 11-Sep-87 04:28:59 EDT
Article-I.D.: sun.27742
Posted: Fri Sep 11 04:28:59 1987
Date-Received: Sat, 12-Sep-87 16:32:55 EDT
References: <197@tiger.Princeton.EDU>
Organization: Sun Microsystems, Inc. - Mtn View, CA
Lines: 22
Keywords: NULLFUNC

> If p is declared as :
> struct x
> { int (*p)(); };
> Now I want to initialize a variable y which is a structure x.
> struct x y = { NULLFUNC };
> The question is what should I put into the #define NULLFUNC .... ?
> (I am using Microsoft C 4.0). Thanks for your help.

Unless Microsoft C 4.0 is badly broken, "#define NULLFUNC 0" should suffice;
the compiler knows enough to coerce the "0" to a pointer of the appropriate
type, and should do so in this context if it claims to implement C.  NULL
should also suffice, if it is defined as 0 or (sigh) 0L.

If you want to pass a null pointer of the same type as the member of "x" to a
function, and there is no prototype for that function in scope, you have to
use a cast, as the compiler *doesn't* know enough to coerce "0" to a pointer
of the appropriate type in that context.  In that case, the properly-cast
pointer is "(int (*)())0".
-- 
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com (or guy@sun.arpa)