How C++ compiler knows the length of an array

For example, in the main function, I can write int arr[42], and I can use range for loop without indicating its length for (auto i : arr). It works well. Compiler will know its length.

If I pass this array to another function, such as void foo(int arr[]), I cannot use range for loop because the compiler doesn't know its length.

After all, if I have this template template<class T, size_t N> void arr_init(T (&foo)[N]), I can call it by arr_init(x). Obviously, the compiler calls arr_init(int (&)[42]).

I guess the compiler knows the length of array through its declaration int[42]. Am I right? I've got this question when I use range for loop and learn templates. I haven't met such problem before, when I was using C.