From owner-freebsd-current  Thu Mar 12 19:39:45 1998
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From: "Jonathan M. Bresler" <jmb>
Message-Id: <199803130339.TAA10294@hub.freebsd.org>
Subject: Re: A question about sys/sys/queue.h
In-Reply-To: <XFMail.980312191745.shimon@simon-shapiro.org> from Simon Shapiro at "Mar 12, 98 07:17:45 pm"
To: shimon@simon-shapiro.org
Date: Thu, 12 Mar 1998 19:39:39 -0800 (PST)
Cc: freebsd-current@FreeBSD.ORG
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Simon Shapiro wrote:
> Why was the definition of some macros changed
> from:
> 
> #define FOO {   ...   }
> 
> to:
> 
> #define FOO do {  ...  } while(0)
> 
> I thought these are the same...
> 

	the difference lies in how you use them.
	in the first case one writes "FOO"
	in the second "FOO;"
			  ^
	make a macro act more like a statement.

	imagine the code around the macro
	rather then the macro itself.

	first saw this in _C_traps_and_pitfalls_
	by andrew koenig (sp?)
jmb

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