nested class 例子

#include<iostream> 

using namespace std; 

/* start of Enclosing class declaration */
class Enclosing {
private:
    int x; 

    /* start of Nested class declaration */
    class Nested {
    public:
        int y;
        void NestedFun(Enclosing *e) {
            cout<<e->x; // works fine: nested class can access
                        // private members of Enclosing class
        }
    }; // declaration Nested class ends here
    public:
    int access_nested(){
        Nested nested;
        cout<<nested.y<<endl;
        return ;
    }
}; // declaration Enclosing class ends here 

int main()
{
    Enclosing enclosing_instance;
    enclosing_instance.access_nested();
}