C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Semantics of tr1::array::data when size is 0?          C++Talk.NET Forum Index -> C++ language, library and standards View previous topic :: View next topic   Author Message Scott Meyers Guest Posted: Wed Feb 08, 2006 3:17 pm    Post subject: Semantics of tr1::array::data when size is 0? What are the semantics of tr1::array::data when the size of the array is zero? The June 2005 TR1 draft (n1836) doesn't seem to say, nor is there any information on this topic in clause 23.1 of the 2003 standard, which TR1 refers to. 21.3.6 says that string::data returns a non-null pointer for a zero-length string, but Nicolai Josuttis' implementation of tr1::array (http://www.josuttis.com/cppcode/array.hpp.html) has array::data return NULL when size is zero. (This is relevant only because a comment in the source file says it was updated to bring it into sync with TR1.) So what are the semantics of tr1::array<T, 0>::data, and where is this specified? Thanks, Scott --- [ 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 ] Back to top sebor@apache.org Guest Posted: Wed Feb 08, 2006 11:38 pm    Post subject: Re: Semantics of tr1::array::data when size is 0? IIRC, the semantics should be the same as begin() and end() in that case. I.e., data() should return a unique (but not derefernceable) pointer. I'm not sure why it's not specified in the text; it should be. --- [ 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 ] Back to top Pete Becker Guest Posted: Thu Feb 09, 2006 12:10 am    Post subject: Re: Semantics of tr1::array::data when size is 0? Scott Meyers wrote: Quote: So what are the semantics of tr1::array<T, 0>::data, and where is this specified? That's Issue 8.6 in N1809. -- Pete Becker Dinkumware, Ltd. (http://www.dinkumware.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.jamesd.demon.co.uk/csc/faq.html ] Back to top Howard Hinnant Guest Posted: Sun Feb 12, 2006 3:06 am    Post subject: Re: Semantics of tr1::array::data when size is 0? In article <11uid2ud7jmj411 (AT) corp (DOT) supernews.com>, Scott Meyers <usenet (AT) aristeia (DOT) com> wrote: Quote: So what are the semantics of tr1::array<T, 0>::data, and where is this specified? Purposefully unspecified: http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#519 -Howard --- [ 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 ] Back to top Pete Becker Guest Posted: Sun Feb 12, 2006 10:29 pm    Post subject: Re: Semantics of tr1::array::data when size is 0? Howard Hinnant wrote: Quote: In article <11uid2ud7jmj411 (AT) corp (DOT) supernews.com>, Scott Meyers <usenet (AT) aristeia (DOT) com> wrote: So what are the semantics of tr1::array<T, 0>::data, and where is this specified? Purposefully unspecified: http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#519 Not purposefully. Accidentally. The DR is intended to clear this up. -- Pete Becker Dinkumware, Ltd. (http://www.dinkumware.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.jamesd.demon.co.uk/csc/faq.html ] Back to top sebor@roguewave.com Guest Posted: Mon Feb 13, 2006 12:13 am    Post subject: Re: Semantics of tr1::array::data when size is 0? Why did we leave it unspecified when begin() and end() are? --- [ 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 ] Back to top Howard Hinnant Guest Posted: Mon Feb 13, 2006 8:06 pm    Post subject: Re: Semantics of tr1::array::data when size is 0? In article <1139779927.795010.298760 (AT) z14g2000cwz (DOT) googlegroups.com>, "sebor (AT) roguewave (DOT) com" <sebor (AT) roguewave (DOT) com> wrote: Quote: Why did we leave it unspecified when begin() and end() are? From the current resolution of lwg 519 it looks to me like all of begin(), end() and data() are unspecified, except that begin() == end(). I believe the rationale is so that an implementation can be as efficient as possible. An invariant is that the client can not dereference any of these entities, and nothing more is assumed. -Howard --- [ 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 ] Back to top sebor@roguewave.com Guest Posted: Thu Feb 16, 2006 5:49 pm    Post subject: Re: Semantics of tr1::array::data when size is 0? begin() and end() are specified to return a *unique* value. Assuming that means a value distinct from any other object's begin() and end(), why not specify the same thing for data()? Wouldn't returning this be just as efficient as returning 0? --- [ 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 ] Back to top Guest Posted: Thu Feb 23, 2006 10:01 pm    Post subject: Re: Semantics of tr1::array::data when size is 0? sebor (AT) apache (DOT) org wrote: Quote: IIRC, the semantics should be the same as begin() and end() in that case. I.e., data() should return a unique (but not derefernceable) pointer. I'm not sure why it's not specified in the text; it should be. If tr1::array is supposed to behave like an array, shouldn't a 0 size be a compile error? --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. 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