File.readAsString

Learn to read files with File.readAsString.

Reading a file as a string

File.readAsStringSync() reads a file's full content as a string. It is synchronous; the program waits until done. Write to the file first, then read.

The async readAsString() returns a Future<String>; you wait with await. For small files the synchronous version is simpler.

If the file is missing the read throws. So checking with existsSync() first is safer.

Encoding

readAsStringSync() uses UTF-8 encoding by default. Special characters read correctly. You can pass another encoding with readAsStringSync(encoding: latin1).

Writing with writeAsStringSync('text') also uses UTF-8. Inconsistent encoding garbles characters and makes them unreadable.

Dart strings are Unicode based; emojis and special letters travel safely. As long as the file is encoded right, the letters stay intact.

Exercise Write then read

Import the library with import 'dart:io';. In main create File('data.txt'); write with writeAsStringSync('Dart 3'). Then read with readAsStringSync() and print it with print.

Show example solution

import 'dart:io';

void main() {
  var f = File('data.txt');
  f.writeAsStringSync('Dart 3');
  print(f.readAsStringSync());
}

Test yourself

What does readAsStringSync() return?
- A bool
- A Future
- An int
- A string (String)
Show answer

A string (String) — readAsStringSync() returns a string.

The readAsStringSync call

var f = File('not.txt');
var content = f.____();

Show answer

var f = File('not.txt');
var content = f.readAsStringSync();

Reading parts

readAsStringSync()

Sync reading
readAsString()

Async reading
Future<String>

Async return
UTF-8

Encoding

Next lesson: File.writeAsString

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