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From: mark@jhereg.Minnetech.MN.ORG (Mark H. Colburn)
Newsgroups: gnu.gcc
Subject: Re: #pragma once
Message-ID: <305@jhereg.Minnetech.MN.ORG>
Date: 8 Nov 89 13:46:26 GMT
References: <8910300524.AA11104@sugar-bombs.ai.mit.edu> <1989Nov1.094352.24529@paris.ics.uci.edu> <522@loft386.UUCP>
Reply-To: mark@jhereg.UUCP (Mark H. Colburn)
Distribution: gnu
Organization: Open Systems Architects, Inc., Mpls, MN
Lines: 34

In article <522@loft386.UUCP> dpi@loft386.UUCP (Doug Ingraham) writes:
>#ifdef __GNUC__
>#pragma once
>#endif
>#ifndef __STRING_H
>#define __STRING_H
>
>< The required string.h information here >
>
>#endif	/* __STRING_H */

Ok, I'll finally admit it, I am a little confused as to why there is such a
construct as the #pragma once.

If you want to avoid including the file twice, why not use the "standard"
method of enclosing the entire thing in "#ifdefs" as shown above:

	#ifndef __MYHEADER_H
	#define __MYHEADER_H

		<header stuff>

	#endif /* __MYHEADER_H */

This works on any machine with a preprocessor, is portable across any
compiler, does not use a #pragma, and is in widespread use today.  Also,
from the discussion which has ensued here about #pragma once, I assume that
it does not always work correctly.

Can someone enlighten me here?

-- 
Mark H. Colburn                       mark@Minnetech.MN.ORG
Open Systems Architects, Inc.