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

struct A {
};

struct B : public A {
  int x;
};

void f( A a ) {
   // in here you can't access any of B's members - they have ben sliced
}

int main() {
    B b;
    f( b );   // slice!
}