Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933210AbWLaUTM (ORCPT ); Sun, 31 Dec 2006 15:19:12 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933211AbWLaUTL (ORCPT ); Sun, 31 Dec 2006 15:19:11 -0500 Received: from nic.NetDirect.CA ([216.16.235.2]:38915 "EHLO rubicon.netdirect.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933210AbWLaUTK (ORCPT ); Sun, 31 Dec 2006 15:19:10 -0500 X-Originating-Ip: 74.109.98.100 Date: Sun, 31 Dec 2006 15:13:59 -0500 (EST) From: "Robert P. J. Day" X-X-Sender: rpjday@localhost.localdomain To: Muli Ben-Yehuda cc: Linux kernel mailing list , Randy Dunlap , trivial@kernel.org Subject: Re: [PATCH] Documentation: Explain a second alternative for multi-line macros. In-Reply-To: <20061231200903.GF3730@rhun.ibm.com> Message-ID: References: <20061231194501.GE3730@rhun.ibm.com> <20061231200903.GF3730@rhun.ibm.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Net-Direct-Inc-MailScanner-Information: Please contact the ISP for more information X-Net-Direct-Inc-MailScanner: Found to be clean X-Net-Direct-Inc-MailScanner-SpamCheck: not spam, SpamAssassin (not cached, score=-16.8, required 5, autolearn=not spam, ALL_TRUSTED -1.80, BAYES_00 -15.00) X-Net-Direct-Inc-MailScanner-From: rpjday@mindspring.com Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1846 Lines: 56 On Sun, 31 Dec 2006, Muli Ben-Yehuda wrote: > On Sun, Dec 31, 2006 at 02:49:48PM -0500, Robert P. J. Day wrote: > > > there would appear to be *lots* of cases where the ({ }) notation > > is used when nothing is being returned. i'm not sure you can be > > that adamant about that distinction at this point. > > IMHO, the main point of CodingStyle is to clarify how new code > should be written and old code should've been written. ok, how about this as a patch: diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index 9069189..064a13e 100644 --- a/Documentation/CodingStyle +++ b/Documentation/CodingStyle @@ -549,13 +549,26 @@ may be named in lower case. Generally, inline functions are preferable to macros resembling functions. -Macros with multiple statements should be enclosed in a do - while block: - -#define macrofun(a, b, c) \ - do { \ - if (a == 5) \ - do_this(b, c); \ - } while (0) +There are two techniques for defining macros that contain multiple +statements, depending on whether you're returning a value or not: + + (a) If there is no return value from the macro, you should enclose + the statements in a do - while block, as in: + + #define macrofun(a, b, c) \ + do { \ + if (a == 5) \ + do_this(b, c); \ + } while (0) + + (b) If the macro is designed to return a value, you should use the + gcc extension that a compound statement enclosed in parentheses + represents an expression, as in: + + #define maxint(a, b) ({ \ + int _a = (a), _b = (b); \ + _a > _b ? _a : _b; \ + }) Things to avoid when using macros: - 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/