C++@类的静态成员变量和静态成员函数

class Point  
{  
public:   
    void init()  
    {    
    }  
    static void output()  
    {  
    }  
};  
void main()  
{  
    Point::init();  
    Point::output();  
}  
//编译出错：error C2352: ‘Point::init‘ : illegal call of non-static member function

//上述main()可以改为
void main()  
{  
    Point pt;  
    pt.init();  
    pt.output();  
}  
//编译通过

#include <stdio.h>  
class Point  
{  
public:   
    void init()  
    {    
    }  
    static void output()  
    {  
        printf("%d\n", m_x);  
    }  
private:  
    int m_x;  
};  
void main()  
{  
    Point pt;  
    pt.output();  
}  
//编译出错：error C2597: illegal reference to data member ‘Point::m_x‘ in a static member function

class Point  
{  
public:   
    void init()  
    {    
        output();  
    }  
    static void output()  
    {  
    }  
};  
void main()  
{  
    Point pt;  
    pt.output();  
}  
//编译通过

#include <stdio.h>  
class Point  
{  
public:   
    Point()  
    {    
        m_nPointCount++;  
    }  
    ~Point()  
    {  
        m_nPointCount--;  
    }  
    static void output()  
    {  
        printf("%d\n", m_nPointCount);  
    }  
private:  
    static int m_nPointCount;  
};  
void main()  
{  
    Point pt;  
    pt.output();  
}  
//编译通过，运行错误。改正：在main()函数前加上int Point::m_nPointCount = 0;

class base{ 
public : 
static int _num;//声明 
}; 
int base::_num=0;//静态数据成员的真正定义 

class derived:public base{ 
}; 

main() 
{ 
base a; 
derived b; 
a._num++; 
cout<<"base class static data number _num is"<<a._num<<endl; 
b._num++; 
cout<<"derived class static data number _num is"<<b._num<<endl; 
} 
// 结果为1,2;可见派生类与基类共用一个静态数据成员。 

class base{ 
public : 
static base _object1;//正确，静态数据成员 
base _object2;//错误 
base *pObject;//正确，指针 
base &mObject;//正确，引用 
}; 

class base{ 
static int func1(); 
int func2(); 
}; 
int (*pf1)()=&base::func1;//普通的函数指针 
int (base::*pf2)()=&base::func2;//成员函数指针 

class base{ 
virtual static void func1();//错误 
static void func2() const;//错误 
static void func3() volatile;//错误 
};