C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  "realloc" without copying          C++Talk.NET Forum Index -> C++ language, library and standards View previous topic :: View next topic   Author Message Frederick Gotham Guest Posted: Tue Oct 24, 2006 9:22 pm    Post subject: "realloc" without copying It seems there is more than one application for a "realloc" function which doesn't copy over the original data if the memory chunk should be relocated. Any chance of adding such a function to the language? -- Frederick Gotham --- [ 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.comeaucomputing.com/csc/faq.html ] Back to top Andrei Polushin Guest Posted: Tue Oct 24, 2006 9:22 pm    Post subject: Re: "realloc" without copying Frederick Gotham wrote: Quote: It seems there is more than one application for a "realloc" function which doesn't copy over the original data if the memory chunk should be relocated. Any chance of adding such a function to the language? And perhaps even a "realloc_check" function which would check whether it is necessary to reallocate the buffer? Note that "reallocate" is not identical to "relocate". It may relocate to prevent memory fragmentation or just for fun :) "realloc_check" is simply harmful, because you may get "true" for the first call, and "false" for the second call (due to multithreading). Isn't it better to customize realloc with move handler? typedef void(*move_handler)(void* to, const void* from, size_t n); void* _expand_fit(void* p, size_t new_size); // find larger block void* _better_fit(void* p, size_t new_size); // find better block void* realloc(void* p, size_t old_size, size_t new_size, move_handler move) { if (old_size < new_size) { void* r = _expand_fit(p, new_size); if (r != p) { move(r, p, old_size); free(p); } return r; } else { void* r = _better_fit(p, new_size); if (r != p) { move(r, p, new_size); free(p); } return r; } } size_t _mem_size(void* p); // get block size // classic realloc: void* realloc(void* p, size_t new_size) { return realloc(p, _mem_size(p), new_size, (move_handler)memmove); } -- Andrei Polushin --- [ 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.comeaucomputing.com/csc/faq.html ] Back to top Frederick Gotham Guest Posted: Tue Oct 24, 2006 9:39 pm    Post subject: Re: "realloc" without copying Frederick Gotham posted: Quote: It seems there is more than one application for a "realloc" function which doesn't copy over the original data if the memory chunk should be relocated. Any chance of adding such a function to the language? And perhaps even a "realloc_check" function which would check whether it is necessary to reallocate the buffer? -- Frederick Gotham --- [ 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.comeaucomputing.com/csc/faq.html ] Back to top Howard Hinnant Guest Posted: Tue Oct 24, 2006 11:32 pm    Post subject: Re: "realloc" without copying In article <har%g.15176$j7.332517 (AT) news (DOT) indigo.ie>, fgothamNO (AT) SPAM (DOT) com (Frederick Gotham) wrote: Quote: Frederick Gotham posted: It seems there is more than one application for a "realloc" function which doesn't copy over the original data if the memory chunk should be relocated. Any chance of adding such a function to the language? And perhaps even a "realloc_check" function which would check whether it is necessary to reallocate the buffer? Your timing is impeccable. WG14 discussed this yesterday: http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1085.htm I'm not certain what their decision will be on it. But I believe some support has been voiced for at least a subset of this proposal. -Howard --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. 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