C++ - Singleton Class

---

If there is a need to create only one instance of a class, then make sure,
1. Default and Copy constructors are declared as private.
2. Assignment operator is declared as private.
3. Have a static function that will return the pointer to the class.

Source Code

---

#include <iostream>

 

class MySingletonClass {

 

private:

    int m_nValue;

    MySingletonClass() { };

    MySingletonClass(const MySingletonClass& other);

    const MySingletonClass& operator = (const MySingletonClass& other);

 

public:

    static MySingletonClass* m_pMySingletonClass;

    static MySingletonClass* GetInstance()

    {

        if(m_pMySingletonClass == NULL)

            m_pMySingletonClass = new MySingletonClass();

        return m_pMySingletonClass;

    }

 

    int GetValue() const { return m_nValue; }

 

    void SetValue(int nVal) { m_nValue = nVal; }

};

 

MySingletonClass* MySingletonClass::m_pMySingletonClass = NULL;

 

int main()

{

    MySingletonClass *p1 = MySingletonClass::GetInstance();

    MySingletonClass *p2 = MySingletonClass::GetInstance();

    // Both instances will point to the same object

    p1->SetValue(100);

    std::cout << p2->GetValue();

}

Output

---

100

---

---