220 8738 <33e7f669-7720-45ff-8f0e-66e3a4c4d12c@isocpp.org> article Path: news.gmane.org!not-for-mail From: Andrew Tomazos Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: "Raw" preprocessor macro arguments Date: Mon, 20 Jan 2014 04:51:09 -0800 (PST) Lines: 177 Approved: news@gmane.org Message-ID: <33e7f669-7720-45ff-8f0e-66e3a4c4d12c@isocpp.org> References: <3fc9f495-0bb2-4432-bb79-385fe222feab@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_318_20904850.1390222269341" X-Trace: ger.gmane.org 1390222264 26372 80.91.229.3 (20 Jan 2014 12:51:04 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 20 Jan 2014 12:51:04 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBD5KHQXXWYPRBPNX6SLAKGQELUJCHRQ@isocpp.org Mon Jan 20 13:51:12 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-gg0-f197.google.com ([209.85.161.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1W5EJr-0007KJ-2j for gclcip-std-proposals@m.gmane.org; Mon, 20 Jan 2014 13:51:11 +0100 Original-Received: by mail-gg0-f197.google.com with SMTP id q3sf11054721gge.4 for ; Mon, 20 Jan 2014 04:51:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe :content-type; bh=h1pnPgIUrGzgPvbVUVnNbuYN9/iY2kcOz4kSW28o5tc=; b=khdVDJv9bW2DiZChlsPM70/pBjOyJ8k8oK82y5QQ689XSB3bS2T+BHdw96cPpbJRAl XB9B7am0Zvv8uIXDHDWJ25SB0VaB3l/U/2Ph548bcN+LtKr3tWIAypqus0SQSYgxADTB 1AArzN6znqTwlnMzuSP8gIOAMwuRAVWMM2SGuSY7e1reghcnRjEXvmJn9C64eeB8cI+y V0l6hXssvo8zGvATo85MSxsypI8qptd8mt9syV0hNFW+dKqnez+8oNWEkxhJg2pugLN8 ckbawlHRMyNtx9hkwcVy5Y69zOS0arcPjJAaTGggyr9tDGNiVA12pV0WZaUjHrvLS1tx x8ow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:x-original-sender:reply-to:precedence :mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=h1pnPgIUrGzgPvbVUVnNbuYN9/iY2kcOz4kSW28o5tc=; b=Gx44w0xs9msWVLB9cpPUBLrMFeAaB2F0l5NjupXk2VgQI1c/x+gm8O+eyPFflcU/zG nFRshq/btI/hb3uFh7WbnqeSk9pKV3S///efJeAg6TC4qAB49r0mHoGNrgWe8ItZ2u85 HjHOPIZbt0Fbp8ulCdDPTZETpNcBDCNQHNz0fOBj6HU7ZnN1/fNjFvXKxBpDVJ5xT0d9 Tq2ViVEDnaz89W0+rii365usVpRRbC7Fb+cjouLq+ds0r65ibNmVD0kUlGMQmMjxyhOw V4ZJp2Kz+csLbWZIcogD0u1sfNvzbJ4xbhz6p8SQmVA+o+x6qnAJcBmAM3x3PDPX88lw s/2g== X-Gm-Message-State: ALoCoQk3+a64zrvA5c7/1wvXOpO+9m+hMr7OriYa5TUnVsZLcUqqsr/InB6btgUwfmlxWs9lioX8 X-Received: by 10.224.163.71 with SMTP id z7mr6400012qax.5.1390222270222; Mon, 20 Jan 2014 04:51:10 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.47.9 with SMTP id l9ls1017445qga.13.gmail; Mon, 20 Jan 2014 04:51:09 -0800 (PST) X-Received: by 10.140.105.181 with SMTP id c50mr48786qgf.12.1390222269795; Mon, 20 Jan 2014 04:51:09 -0800 (PST) In-Reply-To: <3fc9f495-0bb2-4432-bb79-385fe222feab@isocpp.org> X-Original-Sender: andrewtomazos@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:8738 Archived-At: ------=_Part_318_20904850.1390222269341 Content-Type: text/plain; charset=UTF-8 On Monday, January 20, 2014 9:53:04 AM UTC+1, Vittorio Romeo wrote: > > I would expect the program to print "1, 2, 3" or "1,2,3" - instead, it > fails to compile. In the following... #define RAW(...) __VA_ARGS__ #define STRINGIFY(mArg) #mArg #define MAKE_STRING(mArg) std::string(STRINGIFY(mArg)) An expansion of: MAKE_STRING(RAW(1, 2, 3)) proceeds as follows: 1. First the mArg param to MAKE_STRING is identified. mArg=`RAW(1,2,3)` 2. Then mArg is macro expanded to mArg=`1,2,3` 3. Then mArg is substituted in the MAKE_STRING replacement list producing `std::string(STRINGIFY(1,2,3))` 4. The MAKE_STRING invocation is now complete, and preprocessing restarts. 5. The `STRINGIFY(1,2,3)` invocation is identified, but it has 3 arguments and expects 1. Error, stop. There are several ways to fix this, but you will start heading into the nesting rules and other things of which there is implementation variance. My advice would be to study Clause 16 in the standard and then study the implementation of the Boost.Preprocessor library if you are interested in going deeper into "macro metaprogramming". You should do this before even considering writing a proposal regarding the preprocessor. On Monday, January 20, 2014 9:53:04 AM UTC+1, Vittorio Romeo wrote: > > http://ideone.com/B5hVDS > > This example shows un-intuitive behavior. > The "raw argument" is actually passed as multiple arguments, and does not > expand correctly. > > I would expect the program to print "1, 2, 3" or "1,2,3" - instead, it > fails to compile. > -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. ------=_Part_318_20904850.1390222269341 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On= Monday, January 20, 2014 9:53:04 AM UTC+1, Vittorio Romeo wrote:
<= span style=3D"color: rgb(0, 0, 0); font-family: arial, sans-serif;">I would= expect the program to print "1, 2, 3" or "1,2,3" - instead, it fails to co= mpile.

In the following...

#define RAW(...) __VA_ARGS__
#define STRINGIFY(mArg) #mArg
= #define MAKE_STRING(mArg) std::string(STRINGIFY(mArg))

An expansion of:
=

MAKE_STRING(RAW(= 1, 23= ))<= br>

proceeds as follows:

1. First the mArg param to MAKE_STRING is ide= ntified. mArg=3D`RAW(1,2,3)`
2. Then mArg is macro expanded to mArg=3D`1,2,3`
3. Then m= Arg is substituted in the MAKE_STRING replacement list producing `std::stri= ng(STRINGIFY(1,2,3))`
4. The MAKE_STRING invocation is now complete, and preproces= sing restarts.
5. The `STRINGIFY(1,2,3)` invocation is identified, but it has 3 ar= guments and expects 1.  Error, stop.

There are several ways to fix this, but yo= u will start heading into the nesting rules and other things of which there= is implementation variance.

My advice would be to study Clause 16 in the standar= d and then study the implementation of the Boost.Preprocessor lib= rary if you are interested in going deeper into "macro metaprogramming". &n= bsp;You should do this before even considering writing a proposal regarding= the preprocessor.


On Monday, January 20, 2014 9:53:04 AM UTC+1, Vit= torio Romeo wrote:
http://ideone.com/B5hVDS

This example shows un-intuitive beh= avior.
The "r= aw argument" is actually passed as multiple arguments, and does not expand = correctly.

I would expect the program to print "1, 2, 3" or "1,2,3" - instead, it fa= ils to compile.

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