Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!ut-sally!nather
From: nather@ut-sally.UUCP (Ed Nather)
Newsgroups: net.lang.c
Subject: Calling functions via pointers
Message-ID: <6165@ut-sally.UUCP>
Date: Thu, 30-Oct-86 13:40:11 EST
Article-I.D.: ut-sally.6165
Posted: Thu Oct 30 13:40:11 1986
Date-Received: Fri, 31-Oct-86 01:58:52 EST
Organization: U. Texas CS Dept., Austin, Texas
Lines: 33

A recent posting of the Boyer-Moore string search algorithm, written in C,
contained several assignment statements in which a pointer to a function
was assigned depending on circumstances.  The designated function was then
called to do its thing.  The definition and call looked like this:

   int (*action)();
        .
        .
        .
    if(action(arg1, arg2))
        etc;

and the pcc under 4.3bsd compiled everything without comment.  The C compiler
written by Microsoft (v 3.0) was unhappy with the function call, however,
insisting "action : not a function."
   
A quick look in K&R failed to reveal a call of the above format, but they
suggested one which looks like this:

   if((*action)(arg1, arg2))
        etc;

When I substituted the above form for the original, Microsoft C compiled the
program without complaint and the code executed correctly; the pcc apparently
will accept either format.

Is the original format documented anywhere?  Is it "standard" C or not?

-- 
Ed Nather
Astronomy Dept, U of Texas @ Austin
{allegra,ihnp4}!{noao,ut-sally}!utastro!nather
nather@astro.AS.UTEXAS.EDU