C++ Static function variable

Question

In one of my methods, a function with two parameters is passed, and saved as rightClick. However, because its in a static function, the compiler wants the function to be initialised before. How can i go about this?

Mouse.cpp

void Mouse::clicked(int button, int state, int x, int y)
{
    if(button == GLUT_LEFT_BUTTON) {
        if(state == GLUT_DOWN) {
            isDragging = true;
            CurrentX = x;
            CurrentY = y;
        }
        else
        {
            isDragging = false;
        }
    }
    else if (button == GLUT_RIGHT_BUTTON)
    {
        if (state == GLUT_DOWN)
        {
            isDragging = true;
            rightClick(x,y);
        }
    }

}

void Mouse::setRightClickFunction(void (*func)(int, int))
{
    rightClick = func;
}

The setRightClickFunction is called before click ever is. Except now i'm getting a different problem : "Mouse::rightClick", referenced from: Mouse::clicked(int, int, int, int) in Mouse.o

Do you mean that setRightClickFunction is static and if so, why? If not, what function does the compiler wants initialized, exactly? — user4815162342
– user4815162342, Commented Sep 16, 2013 at 12:06
Pass a valid function (global, in namespace, or static member function) as argument to the setRightClickFunction function, before the clicked handler is called. — Some programmer dude
– Some programmer dude, Commented Sep 16, 2013 at 12:06
You might also want to read about std::function and std::bind. — Some programmer dude
– Some programmer dude, Commented Sep 16, 2013 at 12:06
@DuskFall a typedef would simplify things. I'll leave Angew to write up the answer if he want's, he would have told you the same thing. — john
– john, Commented Sep 16, 2013 at 12:27

Angew is no longer proud of SO · Accepted Answer · 2013-09-16 12:29:13Z

2

Based on your comments, you're getting a linker error about "undefined reference to Mouse::rightClick. This has nothing to do with function pointers. It's just that whenever you declare a static data member in a class, it's only a declaration. You have to define it somewhere (= in exactly one .cpp file).

Assuming your class Mouse looks something like this:

class Mouse
{
  //...
  static void (*rightClick)(int, int);
  //...
};

You should put this line somewhere into Mouse.cpp:

void (*Mouse::rightClick)(int, int) = 0;

That will serve as the definition of the static data member rightClick.

answered Sep 16, 2013 at 12:29

Angew is no longer proud of SO

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