Question

How can I get this function to change what x is pointing to in the following:

void test(const int *x)

Answer 1

void test(const int *x)
{
    *((int *) x) = 42;
}

But if your object pointed at is const, you will invoke undefined behavior, like in:

const int bla = 58;
test(&bla);   // undefined behavior when the function is executed

This is ok:

int blop = 67;
test(&blop);

You rather want to change the prototype of your test function if you intend to modify the object pointed at.