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Applying Strings, Arrays and Slices

Applying Strings, Arrays and Slices

This lesson discusses relationship of slices with arrays and strings.

We'll cover the following...

Making a slice of bytes or runes from a string

A string in memory is, in fact, a 2 word-structure consisting of a pointer to the string data and the length. The pointer is completely invisible in Go-code. For all practical purposes, we can continue to see a string as a value type, namely its underlying array of characters. If s is a string (so also an array of bytes), a slice of bytes c can immediately be made with

c:=[]byte(s)

This can also be done with the copy-function:

copy(dst []byte, src string)

The for range can also be applied as in the following program:

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package main
import "fmt"
func main() {
  s := "\u00ff\u754c"
  for i, c := range s {
    fmt.Printf("%d:%c ", i, c)
  }
}

We see that with range at line 6 the returned character c from s is in Unicode, so it is a rune. Unicode-characters take 2 bytes; some characters can even take 3 or 4 bytes. If erroneous UTF-8 is encountered, the character is set to U+FFFD and the index advances by one byte.

In the same way as above, the conversion:

c:=[]byte(s)

is allowed. Then, each byte contains a Unicode code point, meaning that every character from the string corresponds to one byte. Similarly, the conversion to runes can be done with:

r:=[]rune(s)

The number of characters in a string s is given by len([]byte(s)). A string may also be appended to a byte slice, like this:

var b []byte
var s string
b = append(b, s...)

Making a substring of a string

The following line:

substr := str[start:end]

takes the substring from str from the byte at index start to the byte at ...