# C++ Object slicing

**[Object slicing](https://en.wikipedia.org/wiki/Object_slicing)** occurs when a derived class object is copied into a base class object by value, silently discarding derived-class members. The code compiles and runs without error, but loses data and polymorphic behavior.

Prevent slicing by passing polymorphic objects by reference or pointer, never by value.

## Example

This example shows how slicing loses derived class data when passing by value.

```cpp
// compile: g++ -o slicing slicing.cpp
// run: ./slicing
// description: demonstrate object slicing when copying derived to base

#include <iostream>

class Animal {
public:
    virtual ~Animal() = default;
    virtual void speak() { std::cout << "Animal sound\n"; }
};

class Dog : public Animal {
public:
    int tricks = 5;
    void speak() override { std::cout << "Woof! (" << tricks << " tricks)\n"; }
};

void processAnimal(Animal a) {  // passed by value: slicing occurs!
    a.speak();
}

int main() {
    Dog dog;
    dog.tricks = 10;
    
    processAnimal(dog);  // Dog sliced to Animal; tricks lost, prints "Animal sound"
    
    return 0;
}
```