Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932085AbXAITXG (ORCPT ); Tue, 9 Jan 2007 14:23:06 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932090AbXAITXF (ORCPT ); Tue, 9 Jan 2007 14:23:05 -0500 Received: from odyssey.analogic.com ([204.178.40.5]:2344 "EHLO odyssey.analogic.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932085AbXAITXE convert rfc822-to-8bit (ORCPT ); Tue, 9 Jan 2007 14:23:04 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-MimeOLE: Produced By Microsoft Exchange V6.5.7226.0 X-OriginalArrivalTime: 09 Jan 2007 19:23:02.0212 (UTC) FILETIME=[946E8840:01C73423] Content-class: urn:content-classes:message Subject: Re: macros: "do-while" versus "({ })" and a compile-time error Date: Tue, 9 Jan 2007 14:23:01 -0500 Message-ID: In-Reply-To: <45A3D1DF.4020205@s5r6.in-berlin.de> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: macros: "do-while" versus "({ })" and a compile-time error Thread-Index: Acc0I5SUJVZddknhTaa+cd5/NsLL0w== References: <45A3D1DF.4020205@s5r6.in-berlin.de> From: "linux-os \(Dick Johnson\)" To: "Stefan Richter" Cc: "Robert P. J. Day" , "Linux kernel mailing list" Reply-To: "linux-os \(Dick Johnson\)" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2250 Lines: 57 On Tue, 9 Jan 2007, Stefan Richter wrote: > Robert P. J. Day wrote: >> just to stir the pot a bit regarding the discussion of the two >> different ways to define macros, > > You mean function-like macros, right? > >> i've just noticed that the "({ })" >> notation is not universally acceptable. i've seen examples where >> using that notation causes gcc to produce: >> >> error: braced-group within expression allowed only inside a function > > And function calls and macros which expand to "do { expr; } while (0)" > won't work anywhere outside of functions either. > >> i wasn't aware that there were limits on this notation. can someone >> clarify this? under what circumstances *can't* you use that notation? >> thanks. > > The limitations are certainly highly compiler-specific. I don't think so. You certainly couldn't write working 'C' code like this: do { a = 1; } while(0); This _needs_ to be inside a function. In fact any runtime operations need to be inside functions. It's only in assembly that you could 'roll your own' code like: main: ret 0 Most of these errors come about as a result of changes where a macro used to define a constant. Later on, it was no longer a constant in code that didn't actually get compiled during the testing. Cheers, Dick Johnson Penguin : Linux version 2.6.16.24 on an i686 machine (5592.72 BogoMips). New book: http://www.AbominableFirebug.com/ _  **************************************************************** The information transmitted in this message is confidential and may be privileged. Any review, retransmission, dissemination, or other use of this information by persons or entities other than the intended recipient is prohibited. If you are not the intended recipient, please notify Analogic Corporation immediately - by replying to this message or by sending an email to DeliveryErrors@analogic.com - and destroy all copies of this information, including any attachments, without reading or disclosing them. Thank you. - 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/