C++嵌套类

C++支持类的嵌套，其语法比较简单。代码是最好的说明。

#include <iostream>
using namespace std;

class Outter{
    public:
        int a;
        static int s;
        //nested class and enclosing class are independent.
        class Inner{ 
            public:
            int b;
            //nested class can access static members of enclosing class
            int foo(){ return b + s;}
            int bar();
        };
};

int Outter::s = 1;
//define a nested class member outside of the class declaration.
int Outter::Inner::bar(){
    return 0xdeadbeef;
}

int main(){
    Outter o;
    o.a = 0;
    //if nested class is specified as public, then everyone can use the nested class.
    //if nested class is specified as protected, then only the enclosing class,
    //friend of the enclosing class and derived class of the enclosing class can access the nested class.
    //if the nested class is specified as private, then only the enclosing class
    //and friend of the enclosing class can access the nested class.
    Outter::Inner i;
    i.b = 1;
    cout<<i.foo()<<endl;
    cout<<hex<<i.bar()<<endl;
    return 0;
}