what is containership or nesting in C

Question

According to what I believed, a class may include objects from another class as member data.

Please provide an illustration.

Thanks.

Answer 1

Class nesting is just having one class specified in another, as in:

class A
{
public:
   class B 
   {
   public:
       class C{};
   };

};

Then, like with namespaces, you can use the scope operator to access a nested class:

A a;
A::B b;
A::B::C c;

It is now an aggregate when one class contains the object of another class:

class D
{
public:

   A myA;

   void do_something();

private:
   A::B myB;

};

If the member is public, you can access it as follows:

D d;
process( d.myA ); // access to myA

If it is not accessible, you can make it available with a function. 

In any case, you may directly access the member from within the class functions:

void D::do_something()
{
    doit( myB );
    // or
    doit( this->myB );