Using object outside class - c++

Question

I'm trying to create some classes containing textures&sprites using SFML.
When I create object of class in SFML library in my class - i cannot use that object in main.
I wonder how to display sprite in main (e.g.):
class MainMenu
{
public:
int DrawMenu(){
sf::Texture texture;
if (!texture.loadFromFile("idle.png"))
return EXIT_FAILURE;
sf::Sprite spritemenu(texture);
return 0;
}
};
int main()
{
// Create the main window
sf::RenderWindow app(sf::VideoMode(800, 600), "SFML window");
// Load a sprite to display
sf::Texture texture;
if (!texture.loadFromFile("cb.bmp"))
return EXIT_FAILURE;
sf::Sprite sprite(texture);
MainMenu menu;
// Start the game loop
while (app.isOpen())
{
// Process events
sf::Event event;
while (app.pollEvent(event))
{
// Close window : exit
if (event.type == sf::Event::Closed)
app.close();
}
// Clear screen
app.clear();
// Draw the sprite
app.draw(sprite);
menu.DrawMenu();
app.draw(spritemenu);
// Update the window
app.display();
}
return EXIT_SUCCESS;
}

Answer 1

Your DrawMenu function name is lying. It doesn't draw anything. It loads the texture and sprite.
DrawMenu should simply draw the menu sprite:
void DrawMenu(sf::RenderWindow& window) { // window = where to draw the menu
window.draw(spritemenu);
}
Now where do you load spritemenu? It stays the same through the lifetime of MainMenu, so it should naturally be instantiated in the constructor of MainMenu:
class MainMenu
{
public:
MainMenu() {
if (!texture.loadFromFile("cb.bmp"))
abort(); // or throw exception
spritemenu.setTexture(texture); // "initialize" spritemenu with texture
}
…
private:
sf::Texture texture; // Store these as member data, so they will be
sf::Sprite spritemenu; // kept alive through the lifetime of MainMenu.
};
Now when you do MainMenu menu; the texture and sprite will be initialized once, and not every time you call the draw function.
And when you need to draw the menu, simply call menu.DrawMenu(app); instead of menu.DrawMenu(); app.draw(spritemenu);.

Answer 2

The best way to do this is probably to pass app as an argument to DrawMenu, something like this:
class MainMenu {
public:
int DrawMenu(sf::RenderWindow& app){
sf::Texture texture;
if(!texture.loadFromFile("idle.png"))
return EXIT_FAILURE;
sf::Sprite spritemenu(texture);
app.draw(spritemenu);
return 0;
}
};
Then call menu.DrawMenu(app) instead of menu.DrawMenu().
Note that it's meaningless to return EXIT_FAILURE from any function other than main(); I suggest throwing an exception instead.
Also, it's silly to reload the menu every time you draw it. I suggest moving the loading to the MainMenu constructor.