Undefined behaviour with const_cast

Question

I was hoping that someone could clarify exactly what is meant by undefined behaviour in C++. Given the following class definition:

class Foo
{
public:
             


        

Answer 1

Undefined behaviour depends on the way the object was born, you can see Stephan explaining it at around 00:10:00 but essentially, follow the code below:

void f(int const &arg)
{
    int &danger( const_cast(arg); 
    danger = 23; // When is this UB?
}

Now there are two cases for calling f

int K(1);
f(k); // OK
const int AK(1); 
f(AK); // triggers undefined behaviour

To sum up, K was born a non const, so the cast is ok when calling f, whereas AK was born a const so ... UB it is.