sdl 2 - How to properly pass a pointer to a function in C++ for another function operating directly on that pointer? -

i learning create c++ applications using sdl2 library , encountered problem while trying organise code.

here's simple example ilustrating situation:

void createwindow (sdl_window *gamewindow) {     gamewindow = sdl_createwindow(/* arguments here */); }  int main (int argc, char* argv[]) {     sdl_window* gamewindow = null;     createwindow(gamewindow);     // code here... } 

why doesn't work? when try compile code, sdl_geterror() screams: "invalid renderer".

when make way

sdl_window* createwindow (sdl_window* gamewindow) {      gamewindow = sdl_createwindow (/* arguments here*/);     return gamewindow; } 

it works. don't way.

i may not understand pointers or way sdl2 works on them, thought passing 1 function lets me operate directly on variables intead of copies, don't have return anything. me looks operating on copy of variable adress, not variable itself.

arguments in c passed value, is, arguments copied , every modification applied arguments in function alters value of that copy, not passed argument.

resolve problem by

• passing reference pointer:

  void createwindow (sdl_window*& gamewindow) {     gamewindow = sdl_createwindow(/* arguments here */); } 

• passing pointer pointer. watch out: c-ish , bad c++ code!

  void createwindow (sdl_window** gamewindow) {     *gamewindow = sdl_createwindow(/* arguments here */); } 

• returning pointer:

  sdl_window* createwindow() {     return sdl_createwindow(/* arguments here */); }