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Nested Classes and Namespaces in C++

1. Nested Classes

A nested class is a class defined within another class. Nested classes are useful when a class needs to use another class that is logically a part of it but not used outside of it.

Nested classes can access private and protected members of their enclosing class, providing a way to encapsulate and organize code more effectively.

#include <iostream>

class Outer {
private:
    int outerData;
public:
    Outer() : outerData(10) {}
    
    // Nested class
    class Inner {
    public:
        void showData(const Outer& obj) {
            std::cout << "Outer Data: " << obj.outerData << std::endl;
        }
    };
};

int main() {
    Outer outer;
    Outer::Inner inner;
    inner.showData(outer); // Nested class accessing private member
    return 0;
}
                    

In this example, the Inner class is nested inside the Outer class. The Inner class has access to the private member outerData of the Outer class and can print it.

2. Namespaces

Namespaces are used to group related classes, functions, and variables to avoid naming conflicts and to provide better organization. They allow you to define scopes for identifiers, helping to prevent collisions in large projects or libraries.

Namespaces are defined using the namespace keyword and can be nested within other namespaces.

#include <iostream>

namespace Outer {
    int value = 5;
    
    namespace Inner {
        void display() {
            std::cout << "Value: " << Outer::value << std::endl;
        }
    }
}

int main() {
    Outer::Inner::display(); // Accessing nested namespace
    return 0;
}
                    

In this example, the Inner namespace is nested within the Outer namespace. The display function in the Inner namespace can access the value from the Outer namespace.