How does one safely static_cast between unsigned int and int?

Question

I have an 8-character string representing a hexadecimal number and I need to convert it to an int. This conversion has to preserve the bit pattern for

Answer 1

unsigned int u = ~0U;
int s = *reinterpret_cast(&u); // -1

Сontrariwise:

int s = -1;
unsigned int u = *reinterpret_cast(&s); // all ones