dart:io

Learn file operations with dart:io.

The dart:io library

The dart:io library provides file, directory and process operations. It is imported with import 'dart:io';. The File class represents files, the Directory class represents folders.

For example File('note.txt') creates a file object. You write to it with writeAsStringSync('Hello') and read it with readAsStringSync().

Note: dart:io does not work on the web platform. It is used in CLI and server apps; on Flutter mobile it is also limited.

File and Directory

File represents a file, Directory a folder. Both come from dart:io. File('a.txt') denotes a file, Directory('data') a folder.

Both have existsSync() for existence and createSync() for creation. Write/read methods are on File, listing on Directory.

Paths use the slash /; for cross-platform paths Dart recommends the path package.

Exercise Write and read a file

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

Show example solution

import 'dart:io';

void main() {
  var f = File('note.txt');
  f.writeAsStringSync('Hello');
  print(f.readAsStringSync());
}

Test yourself

Importing dart:io

import '____';

void main() {}

Show answer

import 'dart:io';

void main() {}

Which classes does dart:io provide?
- Widget and BuildContext
- List and Set
- File and Directory
- Future and Stream
Show answer

File and Directory — dart:io provides the File and Directory classes.
dart:io parts

File('a.txt')

File
Directory('data')

Folder
existsSync()

Existence check
readAsStringSync()

Reading

Next lesson: File.readAsString

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