Date: Thu, 13 Aug 1998 13:09:45 +0200
From: Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Message-Id: <199808131109.NAA15641@acp3bf.physik.rwth-aachen.de>
To: merlin__ AT geocities DOT com (Merlin)
Cc: djgpp AT delorie DOT com
Subject: Re: A very basic question about C programming... diary of a newbie Part 1
Newsgroups: comp.os.msdos.djgpp
Organization: RWTH Aachen, III. physikalisches Institut B
Precedence: bulk

In article <35D2A017 DOT 4808178C AT geocities DOT com> you wrote:


> Eli Zaretskii wrote:

> > On Wed, 12 Aug 1998, Merlin wrote:
> >
> > > void do_nothing();     //these are prototypes
> >
> > No, this isn't a prototype.  This is:
> >
> >   void do_nothing(void);

>   if you leave the void in brackets out it will be assumed..

Wrong. In C, leaving out the argument list completely means you just
wrote an 'old-style' (i.e.: K&R) function declaration, not a
prototype. In detail, it does *not* define the function to take no
arguments at all, it simply doesn't tell anything about the arguments.
That means:

	void do_nothing();

	int main(void) {
          do_nothing(235);
          return 0;
        }

	void do_nothing(foo) 
          int foo;
        {
           foo = foo + foo;
        }

is a valid, correct ANSI-C program. It compiles, links and even works
without any problem or warning message with 'gcc -ansi -pedantic -Wall
-W -g -O'. Change the first line to 'void do_nothing(void);', and gcc
won't even compile it any longer.

C++ is a different case: there '()' means '(void)', which itself is
*illegal*. At least, that's what my lossy memory tells me.


--
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.