C ++：如何访问内部类的方法？

Question

I was going through classes and thought of doing nested classes.So I have the below class declaration.

class myClass {
    public:
        void method1() {
            cout << "This is method 1" << endl;
        }
        class myClass2 {
            void method2() {
                cout << "This is method 2" << endl;
            }
        };
};

As you can see , myClass has a method method2 in it.The code below works just fine and gives me the desired output.

myClass obj;
obj.method1();

But when I try this:

obj.method2();

I get the error message method2 is not a member of myClass .

Questions:

1. Why can't I access the method 'method2 from objects of class myClass`?
2. Is there a way to access method2 ?

For Question 2 , I thought of creating an object of class myClass2 in myClass , then make another function in myClass to access the method2 function.

I want to know if there is any other way out, because my way seems a bit pain staking.

Answer 1

1) Because Class2() is not a member of myClass .

2) You need to instantiate a myClass::myClass2 object and call the member on it. myClass2::Class2() is a member function, so it needs an object to act on. For example

myClass::myClass2 obj;
obj.Class2();

Note that this requires that you make myClass2::Class2() a public member. It is private in your code.

Answer 2

Putting class2 inside of class1 does less than you think it does. It does nothing more than put it in class1 's scope.

So, imagine the same thing but not nested:

class myClass
{
public:
    void Class1()
    {
        cout<<"This is Class 1"<<endl;
    }
};
class myClass2
{
public:
    void Class2()
    {
        cout<<"This is Class 2"<<endl;
    }
};

...

// and this should look normal to you:
myClass obj;
obj.Class1();

myClass2 obj2;
obj2.Class2();

Now put myClass2 in myClass scope, like you did, and see how the last few lines change.

class myClass
{
public:
    void Class1()
    {
      cout<<"This is Class 1"<<endl;
    }
    class myClass2
    {
    public:
        void Class2()
        {
            cout<<"This is Class 2"<<endl;
        }
    };
};

...

myClass obj;
obj.Class1();

myClass::myClass2 obj2;// this is the only thing that changes. You put myClass2 in a different scope.
obj2.Class2();

So to answer your questions directly:

1) Why cant I access the function Class2 using the myClass obj.

Because Class2 is not a member of myClass . It's a member of myClass2 , which you need to instantiate just like you did with myClass .

2) Is there a way to access Class2 function.

Yes, by instantiating a myClass2 , like at the end of my example: myClass::myClass2 obj2; obj2.Class2(); myClass::myClass2 obj2; obj2.Class2(); .