create object by using new, error in compilation

[nickyeng]

I have a class, and i try to create an object of it but it give me error in compilation.

The error is something like "]b]undefined reference to 'Game::PowerUp::powerups[/b]", in constructor of Game::PowerUp.
The error also contain another 2 error : also are undefined reference but under ~PowerUp destructor.

it compiled well actually if i dont create an object of it in test.cpp(main program to create objects), but once i coded this "PowerUp* power = new PowerUp(t, s, 4, 4);" in test.cpp, the compilation fails and give that that error message.

here is my code:

/*** Power Up class ***/
    class PowerUp : public Health {
    public:
        PowerUp(
            const Terrain* t,
            Screen* s,
            unsigned startX,
            unsigned startY,
            unsigned p = STD_POWER_UP
        ) : Health(t, s, startX, startY, p) {
            powerups.insert(this);
        }
            virtual ~PowerUp() { powerups.erase(this); }
            virtual void Use(Character* c) {
                Health::Use(c);
                delete this;    // Powerups disappear once used
            }
            static PowerUp* Find(unsigned atX, unsigned atY) {
                set<PowerUp*>::const_iterator it;
                for (it = powerups.begin(); it != powerups.end(); it++) {
                    if ((*it)->xPos == atX && (*it)->yPos == atY) {
                        return (*it);
                    }
                }
                return 0;
            }
            virtual char GetSymbol() const { return '@'; }
    private:
        unsigned power;
        static set<PowerUp*> powerups;
 

[Ganon11]

Have you initialized the Set powerups in your .cpp file?

[nickyeng]

thanks Ganon11,

i have settled this problem 5 minutes ago.

yes, you're right. I didn't yet initialise the powerups static variable.

Thanks.
Nicky Eng.