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] == 5[a]
Joel says that it’s because of pointer arithmetic but I still don’t understand. Why does a[5] == 5[a] ?
Answer:
The C standard defines the [] operator as follows:
a[b] == *(a + b)
Therefore a[5] will evaluate to:
*(a + 5)and 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[5]” 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).
