C++ Design Patterns

 Singleton Design Pattern -> creational pattern

a class has only one instance, and provide a global point of access to it.

initialization on first use only

//mysingletone.C

#include<iostream>

using namespace std;

class singletone {
        singletone () {} //Constructor made Private
        singletone(const singletone &);  //Copy Constructor Hidden and Not Implemented
public:
        void display();
        static singletone &getstring()  //returns class object singletone
        {
                static singletone singObj;
                return singObj;
        }
};

void singletone::display()    //becomes singletone.display();
{
        cout << "Welcome to Karwar" << endl;
        return;
}
int main()
{
        cout << "singleton code" << endl;
        singletone::getstring().display();

return 0;
}

Result:

singleton code 
Welcome to Karwar

//Singleton Design pattern using reference variable

//singletonwithpointer.C

#include<iostream>

using namespace std;

class singletonRef {
        static singletonRef  *singleObj;
        singletonRef() {}
        singletonRef(const singletonRef &);
public:
        void display ();
        static singletonRef &getstring ()
        {
                if( singleObj == 0)
                singleObj = new singletonRef();
                return *singleObj;
        }
};

singletonRef *singletonRef::singleObj = 0;

void singletonRef::display ()
{
        cout << "Welcome To Karwar" << endl;
}


int main ()
{
        cout << "singleton using pointer" << endl;
        singletonRef::getstring().display ();
        return 0;
}

Result:

singleton using pointer
Welcome to Karwar

//singleton design pattern using Pointer

//singleusingpointer.C

#include<iostream>

using namespace std;

class singletonRef {
        static singletonRef  *singleObj;
        singletonRef() {}
        singletonRef(const singletonRef &);
public:
        void display ();
        static singletonRef *getstring ()
        {
                if( singleObj == 0)
                singleObj = new singletonRef();
                return singleObj;
        }
};

singletonRef *singletonRef::singleObj = 0;

void singletonRef::display ()
{
        cout << "Welcome to Karwar" << endl;
}


int main ()
{
        cout << "singleton using pointer" << endl;
        singletonRef::getstring()->display ();
        return 0;
}

Result:

singleton using pointer
Welcome to Karwar