Stack overflow at runtime

Question

If the compiler calculates the size of the stack required before runtime, how does a stack overflow occur? At compile time does the compiler calculate the total amount of memory required for stack of the whole program?

Answer 1

No.

A compiler can only know what happens during runtime to some very limited extend. For example it cannot tell how much stack is needed to execute the following function:

void foo() {
    int x = 0;
    std::cin >> x;
    if (x == 42) foo();
}

Stack is a limited resource and if you exceed it you get an stackoverflow.