Use this function to allocate an empty, unpopulated SDL_RWops structure.
Returns a pointer to the allocated memory on success, or NULL on failure; call SDL_GetError() for more information.
Applications do not need to use this function unless they are providing their own SDL_RWops implementation. If you just need a SDL_RWops to read/write a common data source, you should use the built-in implementations in SDL, like SDL_RWFromFile() or SDL_RWFromMem(), etc.
You must free the returned pointer with SDL_FreeRW(). Depending on your operating system and compiler, there may be a difference between the malloc() and free() your program uses and the versions SDL calls internally. Trying to mix the two can cause crashing such as segmentation faults. Since all SDL_RWops must free themselves when their close method is called, all SDL_RWops must be allocated through this function, so they can all be freed correctly with SDL_FreeRW().
This function is available since SDL 2.0.0.