Is type punning arrays of same type but different size allowed?

问题

Is type punning arrays of the same type but with a different size still a violation of strict aliasing?

int arr[4];
int(&ref)[2] = reinterpret_cast<int(&)[2]>(arr);

arr[0] = 0; //write to original
ref[0]; //read from pun

回答1:

We can argue as follows; [expr.reinterpret.cast]/11:

A glvalue expression of type T1 can be cast to the type “reference to T2” if an expression of type “pointer to T1” can be explicitly converted to the type “pointer to T2” using a reinterpret_cast. The result refers to the same object as the source glvalue, but with the specified type.

[conv.array]:

An lvalue or rvalue of type “array of N T” […] can be converted to a prvalue of type “pointer to T”. The result is a pointer to the first element of the array.

I.e. arguably, we have a pointer that points to (not just merely represents the address of) the first element. And it is of that element's type. Thus accessing ref[0] should be defined.

By this logic, it is also fine to write

auto& ref = reinterpret_cast<unsigned(&)[200]>(arr);
std::cout << ref[0];

来源：https://stackoverflow.com/questions/36051008/is-type-punning-arrays-of-same-type-but-different-size-allowed