As Joel points out in Stack Overflow podcast #34, in C Programming Language (aka: K & R), there is mention of this property of arrays in C: a == 5[a]
Joel says that it’s because of pointer arithmetic but I still don’t understand. Why does
a == 5[a] ?
The C standard defines the
 operator as follows:
a[b] == *(a + b)
a will evaluate to:
*(a + 5)
5[a] will evaluate to:
*(5 + a)
and from elementary school math we know those are equal.
This is the direct artifact of arrays behaving as pointers, “
a” is a memory address. “
a” is the value that’s 5 elements further from “
a“. The address of this element is “
a + 5“. This is equal to offset “
a” from “
5” elements at the beginning of the address space (
5 + a).