Dart – Read File as String

To read File as a String in Dart, you can use File.readAsString() method or File.readAsStringSync().

File.readAsString() is an asynchronous method and returns a Future<String>. In your callback function, you get the String with contents of file.

File.readAsStringSync() is a synchronous method and returns the contents of file as a String.

Since asynchronous method does not block the execution of program, while contents of the file are fetched, File.readAsString() is preferred over File.readAsStringSync().

Example – Read File as String

In this example, we shall read a file as string using readAsString(). We use then to handle the Future returned by File.readAsString().

Dart Program

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import 'dart:io';

void main() {
  File('resources/file.txt').readAsString().then((String contents) {
    print('File Contents\n---------------');
    print(contents);
  });
}

Run the program. If reading the file is successful, we shall get contents of the file to the variable String contents. Consequently, we can access this variable.

Output

D:\software\dart-sdk\bin\dart.exe --enable-asserts --enable-vm-service:52528 C:\workspace\DartTutorial\bin\main.dart
Observatory listening on http://127.0.0.1:52528/ugP1OacMnQw=/

File Contents
---------------
Welcome to www.tutorialkart.com.

Process finished with exit code 0

Example – Read File as String Synchronously

In this example, we shall read a file as string synchronously using readAsStringSync(). The program execution shall wait here at readAsStringSync() until all the contents of the File is read and returned as String.

Dart Program

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import 'dart:io';

void main() {
  var contents = File('resources/file.txt').readAsStringSync();
  print('File Contents\n---------------');
  print(contents);
}

Run the program. If reading the file is successful, we shall get contents of the file to the variable String contents.

Output

D:\software\dart-sdk\bin\dart.exe --enable-asserts --enable-vm-service:52663 C:\workspace\DartTutorial\bin\main.dart
Observatory listening on http://127.0.0.1:52663/Hp8acRTRhIw=/

File Contents
---------------
Welcome to www.tutorialkart.com.

Process finished with exit code 0

Conclusion

In this Dart Tutorial, we learned how to read the contents of a file as String in Dart programming language.