C++官方文档-静态成员

#include <iostream>

using namespace std;

class Dummy

{

    public:

        static int n;

        int x;

        Dummy()

                : x()

        {

            n++;

        }

        Dummy(int xx)

                : x(xx)

        {

            n++;

        }

        bool isitem(Dummy const&);

        Dummy& operator=(Dummy const& param);

};

bool Dummy::isitem(Dummy const& param)

{

    if(this == &param)

        return true;

    return false;

}

Dummy& Dummy::operator=(const Dummy& param)

{

    this->x = param.x;

    cout << "=" << endl;

    //this指向等号左边的对象

    return *this;

}

/**

 * In fact, static members have the same properties as non-member variables

 * but they enjoy class scope.

 * For that reason, and to avoid them to be declared several times,

 * they cannot be initialized directly in the class,

 * but need to be initialized somewhere outside it.

 * As in the previous example:

 * 实际上,静态成员和非成员变量一样,只是静态成员在class范围,因为这个原因,为了避免它们声明多次

 * 他们不能直接在类里面初始化,但是需要他们在class外被初始化,比如先前那个例子

 */

int Dummy::n = ;

int main()

{

    Dummy a;

    cout << a.n << endl;

    Dummy b[];

    cout << a.n << endl;

    Dummy* c = new Dummy();

    cout << c->n << endl;

    cout << Dummy::n << endl;

    delete c;

    return ;

}