Why this c++ function can return array’s size correctly?

Question

This is my code.
template < typename T, uint32_t SZ >
constexpr uint32_t len(const T(&array)[SZ])
{
return SZ;
}
when I pass the argument like this.
int a[]={1,2,3,4,5,6};
len(a) == 6;
It return a’s size correctly.
Can someone explain it?
https://code.sololearn.com/c8NcavwgzEB9/?ref=app

Answer 1

why dont use for loop ?
for (int x =0;x<6 ;x++)
{
cout << a[x];

Answer 2

because the size is six is not 5 arrays are starting by their index from 0.

Answer 3

It appears to be counting the number of elements on the array. I changed the type of array to float and added an additional item to the array. The process still returned the correct number of elements.