Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!taumet!steve
From: steve@taumet.com (Stephen Clamage)
Newsgroups: comp.lang.c++
Subject: Re: Problems maintaining header files
Message-ID: <587@taumet.com>
Date: 5 Feb 91 17:36:01 GMT
References: <15917@reed.UUCP> <6107@stpstn.UUCP> <3707@lupine.NCD.COM>
Organization: Taumetric Corporation, San Diego
Lines: 24

rfg@NCD.COM (Ron Guilmette) writes:

>Also note that `#pragma once' is likely to be portable to all existing
>ANSI C environments because ANSI C requires that ANSI C preprocessors
>*must* ignore all #pragmas that they do not understand.

Well, it's portable only in the degenerate sense that a compiler won't
complain if it doesn't recognize #pragma once.  It might merely do
something unintended and possibly harmful.

Consider these cases:

1.  The file must not be included more than once but #pragma once is
ignored.

2.  #pragma once means something entirely different to a particular
compiler (such as turn on Customer Engineer features, which can be
turned off with #pragma offce).

If you want to port programs to different environments, don't rely on
nonstandard features.
-- 

Steve Clamage, TauMetric Corp, steve@taumet.com