From 4060323868671306455 X-Google-Thread: f78e5,60dc9044ee8e77d3 X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Return-Path: X-Authentication-Warning: mulga.cs.mu.OZ.AU: fjh set sender to devnull@stump.algebra.com using -f Path: g2news1.google.com!news2.google.com!newsfeed.stanford.edu!comp-std-cpp-robomod!not-for-mail X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) Delivered-To: std-c++@ucar.edu From: "msalters" Newsgroups: comp.std.c++ Subject: Re: Strange new/new() problem Organization: http://groups.google.com Message-ID: <1106038227.037429.135930@c13g2000cwb.googlegroups.com> References: <41ec486b$1@solnews.wv.mentorg.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" X-Trace: posting.google.com 1106038232 32165 127.0.0.1 (18 Jan 2005 08:50:32 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Tue, 18 Jan 2005 08:50:32 +0000 (UTC) User-Agent: G2/0.2 Complaints-To: groups-abuse@google.com Injection-Info: c13g2000cwb.googlegroups.com; posting-host=212.123.206.71; posting-account=G8Vn6AwAAAAe3s4qFj7nFOuhEuzTNEir X-Spamscanner: mailbox7.ucsd.edu (v1.5 Dec 3 2004 17:34:44, -2.8/5.0 3.0.0) X-MailScanner: PASSED (v1.2.8 94742 j0I8oWkY006113 mailbox7.ucsd.edu) X-Virus-Scanned: by amavisd-new at cs.mu.OZ.AU Approved: Fergus Henderson , moderator of comp.std.c++ X-Virus-Scanned: by amavisd-new at cs.mu.OZ.AU Date: Tue, 18 Jan 2005 10:34:35 CST Xref: g2news1.google.com comp.std.c++:3904 "Fedor G. Pikus" wrote: > Consider this example: > struct data { /****/ }; > int main() { > data** p = new (data*)[5]; > } > > What the programmer wanted is to allocate an array of pointers, of > course, and the parenthesis are unnecessary but arguably make reading > the code easier. In this case, yes. 5.3.4/3 shows precisely why parenthesis are sometimes needed. > GCC compiled the code just fine, and did what the programmer wanted, but > several other compilers refused. Error messages are of two types: either > it's "cannot assign data* to data**" or "[5] is unexpected". Comeau > falls into the first cathegory, and I usually trust Comeau to get it > right. Both messages suggest that these compilers interpret this code as > the placement new with "data *" being the location, even though it's a > type, not a variable. There are two possible forms of a new-expression: new new-placement_opt new-type-id new-initializer_opt new new-placement_opt( typeid ) new-initializer_opt Your form is /not/ the latter. [5] cannot be parsed as a new-initializer. The next step is to look at the new-type-id which has the form type-specifier_seq new-declarator_opt type-specifier_seq is just a sequence of type-specifier's. There are quite a number of possible type-specifier's, but none start with a (. The optional new-placement part /does/ start with an (, so the confusion of the compiler is fully understandable. HTH, Michiel Salters --- [ 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 ]