C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  How does "delete [] <pointer>" work?          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message mkaushik Guest Posted: Sun Aug 20, 2006 9:10 am    Post subject: How does "delete [] <pointer>" work? Hi everyone, Im just starting out with C++, and am curious to know how "delete [] <pointer>", knows about the number of memory locations to free. I read somewhere that delete frees up space assigned to <pointer> by "new". Does "new" create a list of pointer names and the size of the memory array they point to? I also read that some compilers may store the number of consec mem locations a pointer points to, just before the first data element. Is that correct? Also, if i used malloc() to make <pointer> point to a number of memory locations, will calling "delete [] <pointer>" still work? if yes, how does delete here know the number of memory locations to free? does the malloc() implementation in C++ also create a pointer/memsize list like "new"? And lastly, if i made another pointer <pointer2> point to the same location as <pointer>, would calling "delete [] <pointer2>" still free up the correct number of locations? Thanks in advance for answering my deluge of questions! regards, Mayank Back to top red floyd Guest Posted: Sun Aug 20, 2006 9:10 am    Post subject: Re: How does "delete [] <pointer>" work? mkaushik wrote: Quote: Hi everyone, Im just starting out with C++, and am curious to know how "delete [] pointer>", knows about the number of memory locations to free. The answer is implementation dependent. Quote: I read somewhere that delete frees up space assigned to <pointer> by "new". Does "new" create a list of pointer names and the size of the memory array they point to? I also read that some compilers may store the number of consec mem locations a pointer points to, just before the first data element. Is that correct? In general, that's how it works, but you can't rely on it. Each implementation has its own methods. Quote: Also, if i used malloc() to make <pointer> point to a number of memory locations, will calling "delete [] <pointer>" still work? No. If you malloc() it, free() it. If you "new" it, "delete" it. If you "new[]" it, "delete[]" it. It's that simple. if yes, how Quote: does delete here know the number of memory locations to free? does the malloc() implementation in C++ also create a pointer/memsize list like "new"? Many implementations of operator new call malloc behind the scenes, but it is not required. Again, it's implementation dependent. Besides, you can't delete[] memory allocated with malloc. Quote: And lastly, if i made another pointer <pointer2> point to the same location as <pointer>, would calling "delete [] <pointer2>" still free up the correct number of locations? int* p = new int[30]; int* p2 = p; delete[] p2; Is valid, but dangerous, as p now points at unallocated memory. Accessing anything through p (or p2) is undefined behavior. Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.