LNK2001: Problem ze statycznymi składowymi klasy

class Klasa
{
private:
    static bool initialized;
public:
    inlline static bool isInitialized() {return initialized;}
};

#include <iostream>


class Klasa
{
private:
    static bool initialized;
public:
    inline static bool isInitialized() {return initialized;}
};

bool Klasa::initialized = false;

using namespace std;

int main()
{
    cout<<"Hello World";

    Klasa::isInitialized();

    return 0;
}

class Klasa
{
public:
    inline static bool isInitialized(bool setInit=false)
    {
        static bool initialized=false;
        if(setInit) initialized=true;
        return initialized;
    }
};