C++语言基础例程静态成员-白红宇

问题的提出

现状：n个同类的对象，每一个对象都分别有自己的数据成员，各自有值，互不相干。

期望：希望有某一个或几个数据成员为某类所有对象所共有，以实现数据共享。

方案：用全局变量

#include
     
      using namespace std;int N = 0;class Class{private:   int a;public:   Class(){N++;a=0;}   void add(){N++;}};int main( ){    Class c1, c2;    N=300;    c1.add();    cout<
      
       <

例引用静态数据成员

#include 
     
      using namespace std;class Student{public:    Student(int n,string nam, int a):            num(n),name(nam),age(a) { ++count; }    ~Student() { --count; }    int getCount()   { return count; }private:    static int count;    int num;    string name;    int age;};int Student::count=0;int main( ){    Student stu1(1001,"He",40);    cout<
      
       <
       
        getCount()<

用类名访问静态数据成员

#include 
     
      using namespace std;class Student{public:    Student(int n,string nam, int a):            num(n),name(nam),age(a) { ++count; }    ~Student() { --count; }    int getCount()   { return count; }    static int count;private:    int num;    string name;    int age;};int Student::count=0;int main( ){    cout<
      
       <
       
        getCount()<

为什么出错？

#include 
     
      using namespace std;class Student{public:    Student(int n,string nam, int a):            num(n),name(nam),age(a) { ++count; }    ~Student() { --count; }    int getCount()   { return count; }private:    static int count;    int num;    string name;    int age;};int Student::count=0;int main( ){    cout<
      
       <
       
        getCount()<

静态成员函数

#include 
     
      using namespace std;class Student{public:    Student(int n,string nam, int a):            num(n),name(nam),age(a) { ++count; }    ~Student() { --count; }    static int getCount()   { return count; }private:    static int count;    int num;    string name;    int age;};int Student::count=0;int main( ){    cout<
      
       <
       
        getCount()<

静态成员函数不能处理非静态数据成员

#include 
     
      using namespace std;class Student{public:    Student(int n,string nam, int a):            num(n),name(nam),age(a) { ++count; }    ~Student() { --count; }    static int getCount()           { age++; return count; }private:    static int count;    int num;    string name;    int age;};int Student::count=0;int main( ){    cout<
      
       <
       
        getCount()<