Async and Practical

UTF-8 Decode

Bytes to String

utf8.decode from dart:convert reads a List<int> of byte values and returns the decoded String. For ASCII characters the byte count equals the character count; multi-byte UTF-8 sequences would change that ratio.

Program

Play the program to turn five ASCII bytes into the word Hello.

utf8_decode.dart
Replay: real traced execution (multi-file project)
import 'dart:convert';

void main() {
  var bytes = [72, 101, 108, 108, 111];
  var text = utf8.decode(bytes);
  var size = bytes.length;
  print('text="$text" bytes=$size');
}

  1. bytes ← [72, 101, 108, 108, 111]

    3void main() {4  var bytes = [72, 101, 108, 108, 111];5  var text = utf8.decode(bytes);
    values this step[72, 101, 108, 108, 111]bytes

  2. text ← Hello

    4var bytes = [72, 101, 108, 108, 111];5var text = utf8.decode(bytes);6var size = bytes.length;
    values this stepHellotext[72, 101, 108, 108, 111]bytes

  3. size ← 5

    5var text = utf8.decode(bytes);6var size = bytes.length;7print('text="$text" bytes=$size');
    values this step5size[72, 101, 108, 108, 111]bytes

  4. print('text="$text" bytes=$size');

    6  var size = bytes.length;7  print('text="$text" bytes=$size');8}
    outputtext="Hello" bytes=5
    values this stepHellotext5size
utf8 codec `utf8` from `dart:convert` is the encoder/decoder for UTF-8 byte sequences.
utf8.decode `utf8.decode(bytes)` turns a `List<int>` of byte values into a Dart `String`.
byte vs char Each ASCII byte maps to one character, so `bytes.length == text.length` here; multi-byte UTF-8 would make these differ.