What is object slicing in C++?

Question

Accepted Answer

**Object slicing** — when a derived object is copied to a base object, derived parts are lost.

```cpp
class Base {
public:
    int x;
    virtual void print() { std::cout << "Base: " << x << "
"; }
};

class Derived : public Base {
public:
    int y;
    void print() override { std::cout << "Derived: " << x << ", " << y << "
"; }
};

Derived d;
d.x = 1; d.y = 2;

// Object slicing!
Base b = d;   // b.x = 1, but y is lost
b.print();     // "Base: 1" — virtual dispatch lost!

// Prevent with pointers/references
Base* bp = &d;    // No slicing
bp->print();       // "Derived: 1, 2"

Base& br = d;     // No slicing
br.print();        // "Derived: 1, 2"

// Prevent with = delete
Base& operator=(const Base&) = delete;
```

**Prevention:**
- Use pointers or references for polymorphism.
- Delete copy assignment if slicing is dangerous.

C++: What is object slicing in C++?