void employee_set_age(struct Employee* employee, int newAge) { // Cast away the const and set it's value, the compiler should optimize this for you (int)&employee->age = newAge; }

I believe that "Casting away the const" is UB [1]

[1]: https://en.cppreference.com/w/c/language/const.html

It's only UB if the pointed to object is actually const (in which case it might live in read-only memory).