How to copy array into part of another in Go?

Question

I am new to Go, and would like to copy an array (slice) into part of another. For example, I have a largeArray [1000]byte or something and a smallArray [10]byte and I want the first 10 bytes of largeArray to be equal to the contents of smallArray. I have tried:

largeArray[0:10] = smallArray[:]

But that doesn't seem to work. Is there a built-in memcpy-like function, or will I just have to write one myself?

Thanks!

@AnschelSchaffer-Cohen I google'd almost exactly that, and this and a few other like it were listed before the official docs. Also, the docs lack examples to help illustrate how it works (I read the docs first, then came here to finally "get it", and yes, I'm new to Go). — Kaos
– Kaos, Commented Jan 15, 2016 at 18:51

peterSO · Accepted Answer · 2011-08-31 06:18:18Z

41

Use the copy built-in function.

package main

func main() {
    largeArray := make([]byte, 1000)
    smallArray := make([]byte, 10)
    copy(largeArray[0:10], smallArray[:])
}

answered Aug 31, 2011 at 6:18

peterSO

168k32 gold badges302 silver badges293 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

jimt Over a year ago

Nitpicky remark: the [:] bit in the copy() call is not necessary.

themue Over a year ago

Does it have to be a copy? Slices can be a kind of overlay of arrays or other slices. So smallSlice := largeArray[0:10] would be enough.

peterSO Over a year ago

@Mue: Yes, the copy is from smallArray to largeArray. You are copying from largeArray to smallSlice [sic].

Bjarke Ebert Over a year ago

Isnt't that actually creating two slices, not two arrays? But I guess the same code works for arrays as well

Louki Sumirniy Over a year ago

To be strictly correct, it would be this for creating those arrays in that example: var largeArray [1000]byte; var smallArray[10]byte. Note that as indicated, copy can write to a subsection of a slice or array, and I think you can omit the range index on the array because it's copying into 0-9 index of largeArray, copy only copies as much as is contained in the second, and limited by the length (not capacity, I think) of the first.

Collectives™ on Stack Overflow

How to copy array into part of another in Go?

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related