C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  _strdup and delete          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message (2b|!2b)==? Guest Posted: Wed Dec 17, 2008 6:19 pm    Post subject: _strdup and delete is it safe to deallocate memory allocated with _strdup? I suspect that _strdup alocates memory using malloc/calloc behind the scenes - what are the dangers of using delete to free _strdup allocated memory? Back to top Jeff Schwab Guest Posted: Wed Dec 17, 2008 6:19 pm    Post subject: Re: _strdup and delete Andrey Tarasevich wrote: Quote: If the memory is allocated with 'malloc/calloc', then you simply cannot deallocate if with 'delete', period. There's not much sense in discussing the "dangers" of trying to do so. I'm not aware of any guarantee that deleting malloc'd memory will not free the memory. In fact, this is exactly what happens on some platforms. "Simply cannot" is overstating the case. Back to top Jeff Schwab Guest Posted: Wed Dec 17, 2008 6:19 pm    Post subject: Re: _strdup and delete (2b|!2b)==? wrote: Quote: is it safe to deallocate memory allocated with _strdup? As Kai-Uwe pointed out, POSIX strdup uses malloc, and you're supposed to free the returned memory. GNU provides an strdupa function that uses memory in the local stack frame, and is freed when the current function returns. Why are you calling _strdup, rather than using std::strings? Quote: I suspect that _strdup alocates memory using malloc/calloc behind the scenes - what are the dangers of using delete to free _strdup allocated memory? At best, your code will be non-portable. At worst, Bad Things can happen (undefined behavior). Back to top Andrey Tarasevich Guest Posted: Wed Dec 17, 2008 6:19 pm    Post subject: Re: _strdup and delete (2b|!2b)==? wrote: Quote: is it safe to deallocate memory allocated with _strdup? Well, the real question is whether you _should_ deallocate that memory, i.e. whether you _own_ it once it is allocated. You have to read the docs in order to find that out. '_strdup' is not a standard function. Quote: I suspect that _strdup alocates memory using malloc/calloc behind the scenes - what are the dangers of using delete to free _strdup allocated memory? If the memory is allocated with 'malloc/calloc', then you simply cannot deallocate if with 'delete', period. There's not much sense in discussing the "dangers" of trying to do so. -- Best regards, Andrey Tarasevich Back to top Kai-Uwe Bux Guest Posted: Wed Dec 17, 2008 6:19 pm    Post subject: Re: _strdup and delete (2b|!2b)==? wrote: Quote: is it safe to deallocate memory allocated with _strdup? I suspect that _strdup alocates memory using malloc/calloc behind the scenes - what are the dangers of using delete to free _strdup allocated memory? The standard does not mention _strdup. The same applies to strdup, which is neither defined in the C++ standard nor in the referenced C standard. However, that seems to be POSIX. According to the man page, it obtains memory via malloc(), and the memory can be released via free(). I suggest, you find the documentation for _strdup. It should say something about this issues. Best Kai-Uwe Bux Back to top        C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1 Powered by phpBB © 2001, 2006 phpBB Group