How to access nested class member function from enclosing class where all the members are public in c++?

I am using nested classes in a sensor library development and running into errors. Below is sample code and explanation.

MainClass.cpp

class MainClass
{
 public:      
     class nested_class;
     void func1(){
       nested_class1.print();
     }
};

NestedClass.cpp

class MainClass::nested_class
{
 public:
      virtual void print() = 0;
};

Nested1.cpp

class nested_class1: virtual public MainClass::nested_class{
    public:
        void print();
};
void nested_class1::print(){
        cout<<"This is for 1\n";
    }

Nested2.cpp

class nested_class2 : virtual public MainClass::nested_class{
    public:
    void print(){
        cout<<"This is  for 2";
    }
};

I am trying to use it to extend the concept of abstraction in my sensor library. But on doing so following is the error: print() was not declared in this scope.

I am newbie to this concept and hence having a hard time finding the issue here. Where am I going wrong here? I can provide more details if required.

Thanks in advance!