I need to check if the game's SDL Window is open before I can start rendering graphics, normally I would know how to this, but the problem is the window is created in the main class, and I need to check if the window is open in the menu class. How do I check if the window is open in an entirely different class?

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    \$\begingroup\$ Hi from StackOverflow! Just a heads-up about crossposting to multiple stacks: it is quite strongly discouraged. About your question, the simplest approach is storing your window pointer inside a global variable :) \$\endgroup\$
    – Quentin
    Oct 24, 2016 at 8:26
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    \$\begingroup\$ Voting to close this; it doesn't seem specific to game development (despite SDL) but is rather a case of sharing state between classes, which is a generic C++ problem. \$\endgroup\$ Oct 24, 2016 at 8:49
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    \$\begingroup\$ @LeComte a generic Object oriented problem, if you want to be more specific \$\endgroup\$
    – Bálint
    Oct 24, 2016 at 8:50
  • \$\begingroup\$ How would you do it in the main class? In which class is the menu instance created? \$\endgroup\$
    – Thomas
    Nov 24, 2016 at 13:52

1 Answer 1


You dont specify if you are using SDL 1.2, or SDL 2. I will explain it with SDL 1.2.

When yo do a

SDL_Surface* = SDL_SetVideoMode(Params...);

to create the window, you set the pointer of the window created in your SDL_Surface* SDL variable.

The function has two returns.

If has been executed successfully, it will return the pointer of the window. If has NOT been executed successfully, it will return 'NULL';

So, yo need to check if the windows was created checking that pointer. I will copy a segment of my code in SDL:

    Window = SDL_SetVideoMode(WindowWidth, WindowHeigth,Bpp, SDL_HWSURFACE | SDL_RESIZABLE);    /// Asigno al Window el puntero asignado de la pantalla creada

    if( Window == NULL )    /// Window inicializado con error
        if(Is_Open) { Log("Inicialize Window error"); } if(Is_Open) { Log(SDL_GetError()); }
        if(Is_Open) { Log("Window", Window); }

Try to read the documentation for each function. Its not hard. Docs for SDL 1.2: https://www.libsdl.org/release/SDL-1.2.15/docs/ for SDL 2: https://wiki.libsdl.org/

And if you are using different functions you have 2 choices, make the variable of the window Global, or, passing by parameter to all your functions.

PD: Sorry for my english!


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