Is it legal to change a nonconst pointer through const such as this?

Question

Consider the following function:

void f(int const* p)
{
    *const_cast<int*>(id(p)) = 0;
}

Is this legal if you assume that you falways receive a parameter int*as a parameter? I do not ask if this is good to do, I just want a strictly formal answer.

I'm a little worried that if you can do this, it will be harder for the optimizer to work using consts. Consider a more confusing example:

// identity, always returns what it gets
uintptr_t id(uintptr_t p)
{
    static unsigned int const ar[5] {0x12345678, 0x87654321, 0x02468ACE, 0xECA86420, 0x88888888};

    for (size_t i = 0; i < 5; ++i)
        p ^= ar[2*i % 5];

    for (size_t i = 0; i < 5; ++i)
        p ^= ar[3*i % 5];

    return p;
}

void f(int const* p)
{
    uintptr_t q = id(reinterpret_cast<uintptr_t>(p));
    *reinterpret_cast<int*>(q) = 0;
}

Would it be legal? And if not, will the parameter change to int* pmake it legal?

Answer 1

, , const_cast . undefined, , const.

f int*, f ? :

void f(int const* a)
void f(int *a)

, , , . , f.