From -7207443753602922843 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,c8441b0648a55331,start X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 2002-01-02 22:11:20 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!news1.optus.net.au!optus!news.mel.connect.com.au!news.unimelb.edu.au!bounce-back From: "Roger Orr" Newsgroups: comp.std.c++ Subject: Defect Report: pointer to array qualification conversions Date: 03 Jan 02 06:10:51 GMT Organization: OR/2 Limited Lines: 68 Approved: Fergus Henderson Message-ID: <1010015542.7310.0.nnrp-14.9e98aa01@news.demon.co.uk> NNTP-Posting-Host: mundook.cs.mu.oz.au X-Trace: ariel.ucs.unimelb.edu.au 1010038271 26628 128.250.29.16 (3 Jan 2002 06:11:11 GMT) X-Complaints-To: news@news.unimelb.edu.au NNTP-Posting-Date: 3 Jan 2002 06:11:11 GMT X-Original-Date: Wed, 2 Jan 2002 23:38:37 -0000 X-Newsreader: Microsoft Outlook Express 4.71.1712.3 X-MimeOLE: Produced By Microsoft MimeOLE V4.71.1712.3 X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUAPDP18+EDnX0m9pzZAQH8kAF8CoUkLeH3Duo8BM9tt+xM4xtWAMbZnTsS OCr7RZrXrIGgMjR1AzL9Qu9ouNzjkWqs =tiV+ Xref: archiver1.google.com comp.std.c++:8762 [Moderator's note: this defect report has been forwarded to the C++ committee. -moderator.] Section 4.4 "Qualification Conversions" [conv.qual] covers the case of multi-level pointers, but does not appear to cover the case of pointers to arrays of pointers. The effect is that arrays are treated differently from simple scalar values. Consider for example the following code: (from the thread "Pointer to array conversion question" begun in comp.lang.c++.moderated) int main() { double *array2D[2][3]; double * (*array2DPtr1)[3] = array2D; // Legal double * const (*array2DPtr2)[3] = array2DPtr1; // Legal double const * const (*array2DPtr3)[3] = array2DPtr2; // Illegal } and compare this code with:- int main() { double *array[2]; double * *ppd1 = array; // legal double * const *ppd2 = ppd1; // legal double const * const *ppd3 = ppd2; // certainly legal (4.4/4) } The problem appears to be that the pointed to types in example 1 are unrelated since nothing in the relevant section of the standard covers it - 4.4 does not mention conversions of the form "cv array of N pointer to T" into "cv array of N pointer to cv T" It appears that reinterpret_cast is the only way to perform the conversion. Artem Livshits proposed a resolution :- "I suppose if the definition of "similar" pointer types in 4.4/4 was rewritten like this: T1 is cv1,0 P0 cv1,1 P1 ... cv1,n-1 Pn-1 cv1,n T and T2 is cv1,0 P0 cv1,1 P1 ... cv1,n-1 Pn-1 cv1,n T where Pi is either a "pointer to" or a "pointer to an array of Ni"; besides P0 may be also a "reference to" or a "reference to an array of N0" (in the case of P0 of T2 being a reference, P0 of T1 may be nothing). it would address the problem. In fact I guess Pi in this notation may be also a "pointer to member", so 4.4/{4,5,6,7} would be nicely wrapped in one paragraph." Roger Orr -- MVP in C++ at www.brainbench.com --- [ 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.research.att.com/~austern/csc/faq.html ]