On Sunday, October 28, 2012 6:26:28 AM UTC+8, Nobody wrote: > On Sat, 27 Oct 2012 07:42:01 -0700, zlchen.ken wrote: > > > > > I have a DLL which written in C language, one of the function is to > > > allocate a structure, fill the members and then return the pointer of > > > the structure. > > > > > > After Python called this function, and done with the returned structure, > > > I would like to free the returned structure. How can I achieve this ? > > > Basically, I tried that I wrote a corresponding free interface in the > > > DLL, it works, but calling the libc.free in Python doesn't work. > > > > > > my_dll.return_structure_ptr.restypes = POINTER(Dummy) res_ptr = > > > my_dll.return_structure_ptr() windll.msvcrt.free(res_ptr) <==== doesn't > > > work, memory violation my_dll.free_dummy_struture(res_ptr) <== This > > > works. > > > > On Windows, a process may have multiple versions of the MSVCRT DLL (which > > provides malloc/free). If an executable or DLL is linked against multiple > > DLLs, each DLL could be using a different version of MSVCRT. > > > > Different versions of MSVCRT may have separate heaps, so anything which > > is allocated with malloc() (or calloc() or realloc()) from a specific > > version of MSVCRT must be passed to free() from the same version of MSVCRT. > > windll.msvcrt refers to the version of MSVCRT against which the Python DLL > > is linked, which isn't necessarily the version against which my_dll is > > linked. > > > > If a function in a DLL returns a pointer to memory which it allocated > > with malloc(), that DLL must also provide a function which can be used to > > free that memory. It can't leave it to the application (or higher-level > > DLL) to call free(), because the application may not be using the same > > version of MSVCRT as the DLL.
Thank you for the details. This is really useful! -- http://mail.python.org/mailman/listinfo/python-list
