Determine the current read/write offset in an SDL_RWops data stream.
Sint64 SDL_RWtell(SDL_RWops *context);
a SDL_RWops data stream object from which to get the current offset
Returns the current offset in the stream, or -1 if the information can not be determined.
SDL_RWtell is actually a wrapper function that calls the SDL_RWops's
seek method, with an offset of 0 bytes from
RW_SEEK_CUR, to simplify application development.
Prior to SDL 2.0.10, this function was a macro.
This function is available since SDL 2.0.10.