c++ - changing const value in C

Question

I find that in the following code snippet

const int i = 2;  
const int* ptr1= &i;  
int* ptr2 = (int*)ptr1;  
*ptr2 =3;

i's value changes to 3. What I could like to know is why is this allowed. What are the situations in which this could become helpful?

Answer 1

It's allowed because you have overruled the constness of ptr1 by casting it to a non-const pointer. This is why casts can be very dangerous.

Note that some compilers, such as GCC, will not allow you to cast away const status like this.