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From: obrien@cs.ucdavis.edu (David E. O'Brien)
Message-Id: <9601080632.AA25848@toadflax.cs.ucdavis.edu>
Subject: Re: cpp construction
To: chuckr@glue.umd.edu (Chuck Robey)
Date: Sun, 7 Jan 1996 22:31:58 -0800 (PST)
Cc: FreeBSD-chat@freebsd.org
In-Reply-To: <Pine.SUN.3.91.960107232459.7194E-100000@cappuccino.eng.umd.edu> from "Chuck Robey" at Jan 7, 96 11:31:27 pm
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> 
> static int      null_node_alloc __P((struct mount *mp, struct vnode *lowervp,
>                                      struct vnode **vpp));
> 
> It's that __P thing, with the double parens, that has me wondering.  I'd 
> really appreciate some help.

Somewhere else (read in a file included before this one) is:

#ifdef __STDC__   /* plus GCC and anything else that understand prototypes */
#   define __P(args)   args
#else
#   define __P(args)   ()
#endif


Thus under FreeBSD we get:
    static int null_node_alloc (struct mount *mp, struct vnode *lowervp,
                                vnode **vpp);

And if we tried this using cc on SunOS 4.x:

    static int null_node_alloc ();


So it is a method for increase portablity between K&R and Ansi-C.

-- David   (obrien@cs.ucdavis.edu)