What does slicing mean in C++?

Question

It is mentioned in C++ FAQ site -- \"larger derived class objects get sliced when passed by value as a base class object\", what does slicing mean? Any sample to demonstrate

Answer 1

Slicing means that the derived class information is lost. The base class parameter forces an object of the base class to created which share the same base-class state as the derived class. E.g:

struct B { int x; };

struct D : B { double y; };

void f(B b) {}

int main() {
  D d;
  f(d);
}

In the function f you will not be able to access D::y.

Edit: Thanks to everyone for editing. Please make sure that the edit adds value. Note that

• For structs the default inheritance is public.
• If you fix the code, make sure you update the body too