From 5722381693495871079 X-Google-Thread: f78e5,6978327f896d5d5b X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII Path: g2news1.google.com!news4.google.com!news3.google.com!news.glorb.com!newsgate.cistron.nl!news.nl.colt.net!colt.net!peer-uk.news.demon.net!kibo.news.demon.net!news.demon.co.uk!demon!stump.algebra.com!devnull From: jdennett@acm.org (James Dennett) Newsgroups: comp.std.c++ Subject: Re: What is the use of the null directive # ? Date: Thu, 19 May 2005 06:39:06 GMT Organization: Cox Communications Lines: 59 Sender: mail2news@demon.net Approved: fjh@cs.mu.oz.au (Fergus Henderson , moderator of comp.std.c++) Message-ID: <9rWie.144$rp.102@fed1read07> References: <607f883e.0406251028.5412fc80@posting.google.com> NNTP-Posting-Host: news.news.demon.net Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: news.demon.co.uk 1116484752 18665 158.152.254.254 (19 May 2005 06:39:12 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Thu, 19 May 2005 06:39:12 +0000 (UTC) X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.7.5) Gecko/20041217 X-MIME-Autoconverted: from 8bit to quoted-printable by mulga.cs.mu.OZ.AU id j4J6d9D4029105 X-Accept-Language: en-us, en X-Virus-Scanned: by amavisd-new at cs.mu.OZ.AU X-Path: comp-std-cpp-robomod!not-for-mail X-Received: (from fjh@localhost) by mulga.cs.mu.OZ.AU (8.12.10+Sun/8.12.9/Submit) id j4J6d6Ae029079; Thu, 19 May 2005 16:39:06 +1000 (EST) X-NNTP-Posting-Date: Thu, 19 May 2005 02:33:41 EDT X-Delivered-To: std-c++@ucar.edu X-Authentication-Warning: fed1read07.mgt.cox.net: news set sender to newsmaster@cox.net using -f X-Newsgroups: comp.std.c++ Xref: g2news1.google.com comp.std.c++:4805 Krzysztof =AFelechowski wrote: > U=BFytkownik "Barry Margolin" napisa=B3 w wiadomo= =B6ci=20 > news:barmar-AEE035.22095526062004@comcast.dca.giganews.com... >=20 >>In article , >>francis@robinton.demon.co.uk (Francis Glassborow) wrote: >> >> >>>In article <607f883e.0406251028.5412fc80@posting.google.com>, Prateek = R >>>Karandikar writes >>> >>>>What is the use of the null-directive # ? >>>> >>>> >>>> 16.7 Null directive [cpp.null] >>>>1 A preprocessing directive of the form >>>> # new-line >>>> has no effect. >>>> >>> >>>It allows implementors to add directives as extensions without having >>>impact on the portability of code using them. >> >>All it says is that the line: >> >># >> >>is ignored. How does that allow an implementor to add something like: >> >>#foobar >> >>? >> >=20 >=20 > It is very simple. >=20 > #ifndef IT_IS_MY_COMPILER > #define foobar > #endif >=20 > If it is not my compiler, the pragma #foobar is reduced to a hash mark = #.=20 > If it is, it remains and my compiler can handle it. Except that macro expansion happens too late for that to work; #foobar is recognized as an (invalid) preprocessor directive before macro expansion is attempted. -- James --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.jamesd.demon.co.uk/csc/faq.html ]