Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932757AbWLaTpG (ORCPT ); Sun, 31 Dec 2006 14:45:06 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932759AbWLaTpF (ORCPT ); Sun, 31 Dec 2006 14:45:05 -0500 Received: from mtagate2.uk.ibm.com ([195.212.29.135]:62331 "EHLO mtagate2.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932757AbWLaTpE (ORCPT ); Sun, 31 Dec 2006 14:45:04 -0500 Date: Sun, 31 Dec 2006 21:45:01 +0200 From: Muli Ben-Yehuda To: "Robert P. J. Day" Cc: Linux kernel mailing list , Randy Dunlap , trivial@kernel.org Subject: Re: [PATCH] Documentation: Explain a second alternative for multi-line macros. Message-ID: <20061231194501.GE3730@rhun.ibm.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1404 Lines: 44 On Sun, Dec 31, 2006 at 02:32:25PM -0500, Robert P. J. Day wrote: > Generally, inline functions are preferable to macros resembling > functions. This should be stressed, IMHO. We have too many macros which have no reason to live. > -Macros with multiple statements should be enclosed in a do - while block: > +There are two techniques for defining macros that contain multiple > +statements. > > -#define macrofun(a, b, c) \ > - do { \ > + (a) Enclose those statements in a do - while block: > + > + #define macrofun(a, b, c) \ > + do { \ > + if (a == 5) \ > + do_this(b, c); \ > + } while (0) > + > + (b) Use the gcc extension that a compound statement enclosed in > + parentheses represents an expression: > + > + #define macrofun(a, b, c) ({ \ > if (a == 5) \ > do_this(b, c); \ > - } while (0) > + }) When giving two alternatives, the reader will thank you if you explain when each should be used. In this case, the second form should be used when the macro needs to return a value (and you can't use an inline function for whatever reason), whereas the first form should be used at all other times. Cheers, Muli - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/