C++ array[index] vs index[array]

Is the possibility of both array[index] and index[array] a compiler feature or a language feature. How is the second one possible?

Answer

The compiler will turn

index[array]

into

*(index + array)

With the normal syntax it would turn

array[index]

into

*(array + index)

and thus you see that both expressions evaluate to the same value. This holds for both C and C++.