[C/C++] What is a static member variable. Static member function?

When learning the idea of ​​object-oriented programming        in C++ , in the characteristics of object-oriented inheritance , in addition to the concepts of classes and objects , class constructors and destructors , and some operations on class instantiation objects , an important concept is static Member variables (static data members) and static member functions .

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Questions: 1. What is a static member variable?

           2. What is a static member function?

           3. In-depth analysis and application

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Static member variables:
1. All objects share the same data
2. Allocate memory at compile stage
3. Declare inside the class, initialize outside the class

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Static member function:

1. All objects share the same function
2. Static member functions can only access static member variables
 

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Code example:

#include<iostream>
using namespace std;

class Person{
    public:

    static void show(){
        m_a=10;
        cout<<m_a;
        cout<<"函数的调用"<<endl;
    }


    static int m_a;
};
int Person::m_a=9;//静态数据成员类内定义类外初始化
int main()
{
    //静态成员函数的调用方法
    //通过对象访问
    Person p;
    p.show();
    //通过类名访问
    Person::show();
    return 0;
}

Consideration case: Can the access rights of the constructor of a class be set to private? ?