Question
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 doesa[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)
a is a pointer to the first element of the array. a[5] is the value that's
5 elements further from a, which is the same as *(a + 5), and from
elementary school math we know those are equal (addition is
commutative).
