From 557418375120098538 X-Google-Thread: 7894ca11fe,40de2bc986604261 X-Google-Attributes: gid7894ca11fe,public,usenet X-Google-NewGroupId: yes X-Google-Language: ENGLISH,ASCII Path: g2news2.google.com!news2.google.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Sun, 04 Oct 2009 02:40:29 -0500 Return-Path: To: (Usenet) From: =?ISO-8859-1?Q?Daniel_Kr=FCgler?= Newsgroups: comp.std.c++ Subject: Re: Templates as default arguments Organization: http://groups.google.com Sender: cppmods@cs.rpi.edu Approved: james.dennett@gmail.com Message-ID: <9ab9b3d4-311c-40a9-ab3f-2f5b69eb782a@l35g2000vba.googlegroups.com> References: Content-Type: text/plain; charset=ISO-8859-1 X-Original-Date: Sat, 3 Oct 2009 07:57:44 -0700 (PDT) X-Submission-Address: std-c++@netlab.cs.rpi.edu Date: Sun, 4 Oct 2009 02:37:32 CST Lines: 59 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-nOmaROhoDd6v0chmn7r1gV/K3Zxwn4K6hil/gb10rsDswMeV8mMsmuvA0Doa8HwjvdHgwM5Mdgjqn5n!KE3gnxPbrbW5bFJlUDzGcHqSRpVo2PSDNiwtTiwdQAA6e7ta0yTaDmO4Ygl364+iJK0je78gmF9G!5F9OGuX28Jioiui3cCEsMRvQy7g= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Xref: g2news2.google.com comp.std.c++:1428 On 2 Okt., 23:21, dps wrote: > Hi, > > I have the following situation: > > template class A > { > A(){} > > }; > > class B > { > public: > B(A arg=A()){} > > } > > The above is pseudo-code and compiles on VS but not on gcc. Gcc > complains about the "3" in the default argument. But if I write > > class B > { > public: > typedef A AD3; > B(AD3 arg=AD3()){} > > there is no problem. Obviously it has to do with the template > instantiation? But why is only the "3" that creates the problem? I don't believe that the "3" is the problem. The example you provided is ill-formed (e.g. private default constructor) and I don't recommend to provide a "pseudo-code" for a situation that causes a problem, because this has the fundamental tendency to hide the actual problem. Pseudo-code makes sense if you want to present a new idea, because it emphasizes your *idea* what the code should do, but is a bad choice for to present a situation which causes a compile or runtime problem, because to solve this one isn't primarily interested to get your idea, but to understand the nature of the problem. It would also be helpful, if you have provided us information about the compiler versions. From what you present here it looks like a compiler error. If the default constructor was actually public and the class definition of B is completed with a semicolon and the code still causes a compiler error, this is a clearly a compiler defect. HTH && Greetings from Bremen, Daniel Kr�gler -- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@netlab.cs.rpi.edu] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ]