singleton c 2b 2b

1class S
2{
3    public:
4        static S& getInstance()
5        {
6            static S    instance; // Guaranteed to be destroyed.
7                                  // Instantiated on first use.
8            return instance;
9        }
10    private:
11        S() {}                    // Constructor? (the {} brackets) are needed here.
12
13        // C++ 03
14        // ========
15        // Don't forget to declare these two. You want to make sure they
16        // are unacceptable otherwise you may accidentally get copies of
17        // your singleton appearing.
18        S(S const&);              // Don't Implement
19        void operator=(S const&); // Don't implement
20
21        // C++ 11
22        // =======
23        // We can use the better technique of deleting the methods
24        // we don't want.
25    public:
26        S(S const&)               = delete;
27        void operator=(S const&)  = delete;
28
29        // Note: Scott Meyers mentions in his Effective Modern
30        //       C++ book, that deleted functions should generally
31        //       be public as it results in better error messages
32        //       due to the compilers behavior to check accessibility
33        //       before deleted status
34};

1#include <iostream>
2
3using namespace std;
4
5class Singleton {
6   static Singleton *instance;
7   int data;
8 
9   // Private constructor so that no objects can be created.
10   Singleton() {
11      data = 0;
12   }
13
14   public:
15   static Singleton *getInstance() {
16      if (!instance)
17      instance = new Singleton;
18      return instance;
19   }
20
21   int getData() {
22      return this -> data;
23   }
24
25   void setData(int data) {
26      this -> data = data;
27   }
28};
29
30//Initialize pointer to zero so that it can be initialized in first call to getInstance
31Singleton *Singleton::instance = 0;
32
33int main(){
34   Singleton *s = s->getInstance();
35   cout << s->getData() << endl;
36   s->setData(100);
37   cout << s->getData() << endl;
38   return 0;
39}