Object Slicing

What Is Object Slicing?

When a derived class object is assigned to a base class object by value (not by pointer or reference), only the base class portion is copied, and the extra members in the derived class are sliced off.

Example

#include <iostream>
using namespace std;

class Base {
public:
    int a = 1;
    virtual void show() {
        cout << "Base: a = " << a << endl;
    }
};

class Derived : public Base {
public:
    int b = 2;
    void show() override {
        cout << "Derived: a = " << a << ", b = " << b << endl;
    }
};

int main() {
    Derived d;
    Base b = d;  // Object slicing happens here
    b.show();    // Calls Base::show(), not Derived::show()
}

Output:

Base: a = 1

Correct Way (Avoid Slicing)

Use pointer or references to handle polymorphism:

Base* bptr = new Derived();
bptr->show();  // Correctly calls Derived::show()
delete bptr;