On Tue, Apr 13, 2004 at 09:45:39AM -0500, Brian Henning wrote: > I have a question about the stdio.h file. > > In the following function signature what does the __P do? > > Why is the __P needed? > > int (*_close) __P((void *));
History. Backwards compatability. This construct dates from the times of K&R C, before the ANSI standard that said function prototypes should contain argument type declarations. If you examine the <sys/cdefs.h> header file, you'll see that macro is designed to expand to either an empty pair of brackets -- () -- which is the old-style prototype, or the string enclosed within it -- (void *) -- which is the "new" style prototype. I say "new" because prototypes like that have been standard for more than 10 years. On any compiler you encounter nowadays that declaration will be resolved to: int (*_close) (void *) meaning _close is a pointer to a function taking an arbitrary pointer as argument and returning an int. Yes -- the __P() construct is pretty much obsolete nowadays, but it's probably more trouble than it's worth to try and strip it out of everything. Cheers, Matthew -- Dr Matthew J Seaman MA, D.Phil. 26 The Paddocks Savill Way PGP: http://www.infracaninophile.co.uk/pgpkey Marlow Tel: +44 1628 476614 Bucks., SL7 1TH UK
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