Two single cases of C + + (a hungry man, lazy type)

1. Russian-Chinese style
   

   
   

#include <iostream>using namespace Std;class a{public:static a& getinstance (void) {return s_instance;    }private:a (int data=0): m_data (data) {} A (a const& that);    int m_data; Static A s_instance;};    A a::s_instance (1234); int main (void) {a& A1 = A::getinstance ();    a& A2 = A::getinstance ();    cout << &a1 << ', ' << &a2 << Endl; return 0;}

This is a singleton with static members.

Because it is a singleton, it is forbidden to create another class A object, and a calls the constructor to create the object, so the class A constructor is placed in the

Private, a A = A::getinstance () calls the copy constructor to create the object, so the copy constructor is placed in private

The interface function static a& getinstance (void), is static, and if non-static, then how to call getinstance

function, so it has to be static.

Note: Static member Object S_instance is a private constructor that can be called (and I don't know why).

2. Lazy Type

#include  <iostream>using namespace std;class a{public:    static  a& getinstance (void) {        if (!s_instance) {             s_instance  = new a (1234 );         }        return  *s_instance;    }    void release (void) {         if (s_counter && --s_counter==0) {             delete this;             s_instance = NULL;        }     }private:    ~a (void) {}    a (int data =  0): m_data (data) {}    a (a const& that);    int m_data;     static int s_counter;    static A* s_instance;}; int a::s_counter = 0; A* a::s_instance = null;int main (void) {    a& a1 =  A::getinstance ();     a& a2 = a::getinstance ();     cout << &a1 <<  ', '  << &a1 << endl;     a1.release ();     a2.release ();    return  0;}

Here is a static member pointer as a singleton, there is nothing to say.

Note: The static member Pointer S_instance, the constructor is called at New A (1234), but when you delete this, the function is not called, whether it is a public destructor or a private destructor (why you cannot call the destructor I don't know)

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Two single cases of C + + (a hungry man, lazy type)