linux-kernel - Re: [PATCH] Documentation: Explain a second alternative for multi-line macros.

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Date:	Mon, 1 Jan 2007 05:31:32 +0100
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Muli Ben-Yehuda <muli@...ibm.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	"Robert P. J. Day" <rpjday@...dspring.com>, trivial@...nel.org
Subject: Re: [PATCH] Documentation: Explain a second alternative for multi-line macros.

>>>   #define setcc(cc) ({ \
>>>     partial_status &= ~(SW_C0|SW_C1|SW_C2|SW_C3); \
>>>     partial_status |= (cc) & (SW_C0|SW_C1|SW_C2|SW_C3); })
>> This _does_ return a value though, bad example.
>
> Where does it return a value?

partial_status |=

> I don't see any uses of it

Ah, that's a separate thing -- it returns a value, it's just
never used.

> And with a small change to put it inside a do-while block
> instead of ({ ... }), it at least builds cleanly.

Well please replace it then, statement expressions should be
avoided where possible (to start with, they don't have well-
defined semantics).


Segher

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