1. Dart
  2. File Handling in Dart
  3. Dart file Handling Practice Questions with Solution

Practice Questions: File Handling in Dart

  1. Write a program to create a new text file named sample.txt.
  2. Demonstrate how to write a string to sample.txt and confirm the operation.
  3. Create a program that reads the contents of sample.txt and prints them to the console.
  4. Modify the program to append a new line to sample.txt.
  5. Write a program to read all lines from sample.txt and print each line individually.
  6. Check if sample.txt exists before attempting to read from it.
  7. Create a directory named files_directory and store sample.txt inside it.
  8. Write a program to delete sample.txt from files_directory.
  9. Demonstrate how to list all files in files_directory.
  10. Write a program to rename sample.txt to renamed_sample.txt.
  11. Create a program that reads a file and counts the total number of lines.
  12. Write a program to read a file and count how many times a specific word appears.
  13. Create a program that handles exceptions when trying to read from a non-existent file gracefully.
  14. Write a program that copies sample.txt to a new file named copy_sample.txt.
  15. Demonstrate how to delete the entire files_directory along with its contents.


Solutions with Code Explanation
 

1. Write a program to create a new text file named sample.txt.

import 'dart:io';

void main() async {
  File file = File('sample.txt');

  try {
    await file.create();
    print('File created successfully.');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code creates a new file called sample.txt. The create() method is called on the File object, and if successful, it prints a confirmation message.

2. Demonstrate how to write a string to sample.txt and confirm the operation.

import 'dart:io';

void main() async {
  File file = File('sample.txt');

  try {
    await file.writeAsString('Hello, Dart!');
    print('Data written to file successfully.');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: The writeAsString() method writes "Hello, Dart!" to sample.txt. If the write operation is successful, it prints a confirmation message.

3. Create a program that reads the contents of sample.txt and prints them to the console.

import 'dart:io';

void main() async {
  File file = File('sample.txt');

  try {
    String contents = await file.readAsString();
    print('File Contents:\n$contents');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code reads the entire content of sample.txt using readAsString() and prints it to the console.

4. Modify the program to append a new line to sample.txt.

 

import 'dart:io';

void main() async {
  File file = File('sample.txt');

  try {
    await file.writeAsString('\nThis is an appended line.', mode: FileMode.append);
    print('Data appended to file successfully.');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: The writeAsString() method is used with FileMode.append to add a new line to the existing content of sample.txt.

5. Write a program to read all lines from sample.txt and print each line individually.

import 'dart:io';

void main() async {
  File file = File('sample.txt');

  try {
    List<String> lines = await file.readAsLines();
    print('File Lines:');
    for (var line in lines) {
      print(line);
    }
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code reads the lines of sample.txt into a list and prints each line individually using a for loop.

6. Check if sample.txt exists before attempting to read from it.

import 'dart:io';

void main() async {
  File file = File('sample.txt');

  if (await file.exists()) {
    String contents = await file.readAsString();
    print('File Contents:\n$contents');
  } else {
    print('File does not exist.');
  }
}

Explanation: Before reading the file, the program checks if it exists using exists(). If the file exists, it reads and prints the contents; otherwise, it informs the user.

7. Create a directory named files_directory and store sample.txt inside it.

import 'dart:io';

void main() async {
  Directory directory = Directory('files_directory');

  try {
    await directory.create();
    File file = File('${directory.path}/sample.txt');
    await file.writeAsString('Hello from inside the directory.');
    print('File created inside the directory successfully.');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code creates a directory called files_directory and then creates sample.txt inside that directory, writing a message to it.

8. Write a program to delete sample.txt from files_directory.

import 'dart:io';

void main() async {
  File file = File('files_directory/sample.txt');

  try {
    await file.delete();
    print('File deleted successfully.');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code deletes sample.txt from the files_directory using the delete() method.

9. Demonstrate how to list all files in files_directory.

import 'dart:io';

void main() async {
  Directory directory = Directory('files_directory');

  try {
    await for (var entity in directory.list()) {
      print(entity.path);
    }
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code lists all files and directories in files_directory using the list() method and prints their paths.

10. Write a program to rename sample.txt to renamed_sample.txt.

import 'dart:io';

void main() async {
  File file = File('files_directory/sample.txt');

  try {
    File renamedFile = await file.rename('files_directory/renamed_sample.txt');
    print('File renamed to: ${renamedFile.path}');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code renames sample.txt to renamed_sample.txt using the rename() method and prints the new path.

11. Create a program that reads a file and counts the total number of lines.

import 'dart:io';

void main() async {
  File file = File('sample.txt');

  try {
    List<String> lines = await file.readAsLines();
    print('Total number of lines: ${lines.length}');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code reads all lines from sample.txt and prints the total count using the length of the list.

12. Write a program to read a file and count how many times a specific word appears.

import 'dart:io';

void main() async {
  File file = File('sample.txt');
  String targetWord = 'Dart';

  try {
    String contents = await file.readAsString();
    int count = RegExp(r'\b$targetWord\b', caseSensitive: false).allMatches(contents).length;
    print('The word "$targetWord" appears $count times.');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code counts occurrences of a specific word (case insensitive) in the file using a regular expression and prints the count.

13. Create a program that handles exceptions when trying to read from a non-existent file gracefully.

import 'dart:io';

void main() async {
  File file = File('non_existent_file.txt');

  try {
    String contents = await file.readAsString();
    print('File Contents:\n$contents');
  } catch (e) {
    print('Error: File not found.');
  }
}

Explanation: This code attempts to read from a non-existent file and catches the exception, providing a user-friendly error message.

14. Write a program that copies sample.txt to a new file named copy_sample.txt.

import 'dart:io';

void main() async {
  File sourceFile = File('sample.txt');

  try {
    File copyFile = await sourceFile.copy('copy_sample.txt');
    print('File copied to: ${copyFile.path}');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code copies sample.txt to copy_sample.txt using the copy() method and prints the new file's path.

15. Demonstrate how to delete the entire files_directory along with its contents.

import 'dart:io';

void main() async {
  Directory directory = Directory('files_directory');

  try {
    await directory.delete(recursive: true);
    print('Directory and its contents deleted successfully.');
  } catch (e) {
    print('Error: $e');
  }
}

Explanation: This code deletes files_directory and all its contents using delete(recursive: true), ensuring that everything inside is removed.

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