C++——静态

一，局部静态变量

#include<iostream>
#include<string>
using namespace std;

class Student
{
    int n;
    string name;
public:
    void set(string thename)
    {
        static int number=0;//局部静态变量，从运行起到代码结束都保存在内存中
        name=thename;
        n=++number;
    }
    void prin(){cout<<name<<"->students are"<<n<<" numbers"<<endl;}
};

void fn()
{
    Student s1;
    s1.set("Jenny");
    s1.prin();//此时number=2,n=2
    Student s2;
    s2.set("Randy");//此时number=3,n=3
    s1.prin();//输出的是s1中的n=2
    s2.prin();//输出的是s2中的n=3
}

void main()
{
    Student s;
    s.set("Smith");
    s.prin();//此时number=1,n=1
    fn();
    s.prin();//输出的是s中的n=1
}

二，静态成员

#include<iostream>
#include<string>
using namespace std;

class Student
{
    static int number;//静态成员，类的所有对象共享
    string name;
public:
    void set(string thename)
    {
        name=thename;
        ++number;
    }
    void prin(){cout<<name<<"->students are"<<number<<" numbers"<<endl;}
};

int Student::number=0;//必须进行初始化

void fn()
{
    Student s1;
    s1.set("Jenny");
    s1.prin();
    Student s2;
    s2.set("Randy");
    s1.prin();
    s2.prin();
}

void main()
{
    Student s;
    s.set("Smith");
    s.prin();
    fn();
    s.prin();
}

三，静态成员函数

#include<iostream>
#include<string>
using namespace std;

class Student
{
    static int number;//静态成员
    string name;
public:
    void set(string thename)
    {
        name=thename;
        ++number;
    }
    static void prin();//静态成员函数，不受对象的牵制
};

int Student::number=0;
void Student::prin(){cout<<number<<" numbers"<<endl;}//不能写成{cout<<name<<number<<endl;}因为静态成员函数可以不捆绑对象调用，所有没有对象的信息name

void fn()
{
    Student s1;
    s1.set("Jenny");
    s1.prin();//number=2
    Student::prin();//number=2
    cout<<endl<<endl;

    Student s2;
    s2.set("Randy");
    s1.prin();//number=3
    s2.prin();//number=3
    Student::prin();//number=3
    cout<<endl<<endl;
}

void main()
{
    Student s;
    s.set("Smith");
    s.prin();//number=1
    cout<<endl;
    fn();
    Student::prin();//number=3
}