C's index[arr] notation

5 pointsby leegaovor 15 Jahren4 comments

I had always assumed that it was merely some strange artifact of the language, until I finally thought about it, and then finally understood:

arr[index] is equivalent to (arr + index), which by the commutative property of addition is equivalent to (index + arr) = index[arr].

Mind = blown

1 comments

marcomonteirovor 15 Jahren

It's not the same as (index + arr). arr is a pointer to the beginning address of a series of particular "types". These types have a specific size in memory. Index increments the pointer by (n * size_of(type)).

arr[index] == arr + (n * size_of(type)) == (n * size_of(type)) + *arr

SamReidHughesvor 15 Jahren

He said it's the same as

    *(index + arr)

which is correct.

C pointer arithmetic already accounts for object sizes.

And it's sizeof, not size_of. And

    arr + x

is completely different from

    x + *arr

And it's a series of "values".

marcomonteirovor 15 Jahren

I don't know what I was on. Proof positive that sleep depravation does not give me more time to be "productive". Thanks for the correction and apologies for my mistake.

Jacquass12321vor 15 Jahren

Always time for a refresher :) http://augustcouncil.com/~tgibson/tutorial/arr.html

[deleted]vor 15 Jahren