Step 1 - Relative paths

import 'dart:io';

void main() {
  final dir = Directory('data');
  if (!dir.existsSync()) {
    dir.createSync(recursive: true);
  }
  final f = File('${dir.path}/app.json');
  f.writeAsStringSync('{}');
  print(f.absolute.path);
}

• dir.path is a string; ${dir.path}/app.json works on POSIX and macOS. On Windows, backslashes appear in path from the platform.

Step 2 - Current directory

import 'dart:io';

void main() {
  print(Directory.current.path);
}

Step 3 - Parent and absolute

import 'dart:io';

void main() {
  final f = File('data/app.json');
  print(f.absolute.path);
}

Good habit

• Keep a single place (constant or small config) for your data directory name.

Practice tasks

• Create data/backups/ and write a second file there.
• List files in a directory with Directory('data').listSync() and print names (handle FileSystemEntity types).