Hacker News Reader

Comment by doppelganger27 | Hacker News Reader

In C (and in all other languages I can think of), an array is actually a pointer to a bunch of memory. Indexing into the array calculates offset from the array pointer, and grabs the item at that offset.

View on HN

Array is not a pointer. Your description of indexing is not correct, neither is the phrase "array pointer" you invented. The machine code produced will calculate the offset differently for a pointer and an array.

Let me clarify with an example. Suppose you have an array:

  int a[10]

There is a section of memory of size sizeof(int) * 10 somewhere, and the variable a is a * int that points to that section. When someone does this:

  int x = a[2]

It is equivalent to:

  int x = *(a+(sizeof(int)*2))

When I said "array pointer" in my previous comment, all it meant was the memory address that the variable (which is an array) points to (in the example, the variable "a")

Edit: missing paren

a is a label, or an alias of a memory address. It is not a pointer. ( Your third example has a mistake, the correct increment is: a+2, because pointer arithmetic increments in object size not byte size )

Read this:http://eli.thegreenplace.net/2009/10/21/are-pointers-and-arr...

Interesting read. Thanks :)

FYI the equivalent Go code would actually copy the whole array on the stack, and so it would be valid if possibly inefficient depending on the size of the array.

...and for anything larger than a small fixed-size array (like the example), you'd avoid data-copying overhead by passing a slice, which is a bounds-checked bundle of pointer and length.

Reply on news.ycombinator.com