How to assign string to bytes array

Question

I want to assign string to bytes array:

var arr [20]byte
str := \"abc\"
for k, v := range []byte(str) {
  arr[k] = byte(v)
}

Have another m

Answer 1

For converting from a string to a byte slice, string -> []byte:

[]byte(str)

For converting an array to a slice, [20]byte -> []byte:

arr[:]

For copying a string to an array, string -> [20]byte:

copy(arr[:], str)

Same as above, but explicitly converting the string to a slice first:

copy(arr[:], []byte(str))

---

• The built-in copy function only copies to a slice, from a slice.
• Arrays are "the underlying data", while slices are "a viewport into underlying data".
• Using [:] makes an array qualify as a slice.
• A string does not qualify as a slice that can be copied to, but it qualifies as a slice that can be copied from (strings are immutable).
• If the string is too long, copy will only copy the part of the string that fits.

---

This code:

var arr [20]byte
copy(arr[:], "abc")
fmt.Printf("array: %v (%T)\n", arr, arr)

...gives the following output:

array: [97 98 99 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] ([20]uint8)

I also made it available at the Go Playground

Answer 2

Piece of cake:

arr := []byte("That's all folks!!")

Answer 3

Ended up creating array specific methods to do this. Much like the encoding/binary package with specific methods for each int type. For example binary.BigEndian.PutUint16([]byte, uint16).

func byte16PutString(s string) [16]byte {
    var a [16]byte
    if len(s) > 16 {
        copy(a[:], s)
    } else {
        copy(a[16-len(s):], s)
    }
    return a
}

var b [16]byte
b = byte16PutString("abc")
fmt.Printf("%v\n", b)

Output:

[0 0 0 0 0 0 0 0 0 0 0 0 0 97 98 99]

Notice how I wanted padding on the left, not the right.

http://play.golang.org/p/7tNumnJaiN