Question

Is it legal to cast a pointer to the first element of an array to a pointer to the entire array?

template<typename T, size_t N>
void whatever(T(&)[N])
{
    std::cout << N << '\n';
}

int main()
{
    int a[10];
    int * p = a;
    whatever(*(int(*)[10])(p));   // <-- legal?
}

This prints 10 on my compiler, but I’m not sure if the C++ standard allows it.

Answer 1

No, it’s not legal(as in it’s Undefined Behavior). A pointer to the whole array is &a not p. Basically, you’re casting one pointer to another. The standard describes all the allowed conversions and this one is not among them.