Read and Write Input in Dart Programming

Dart provides us with a standard library named 'io' which contains different classes and in turn, these classes contains different methods that we can use to read or write input from the terminal.

We import the library in our program by making use of the import command.

Example

Consider the example shown below −

Import 'dart:io';

Writing something to the terminal

We can write something to the terminal by making use of the standard out class (stdout) that is available to us in the 'dart:io' library.

Example

Consider the example shown below −

 Live Demo

import 'dart:io';

void main(List<String> arguments) {
   stdout.write('What is your name?\r
');
}

Output

What is your name?

Note − It should be noted that we run a dart file by running the command: dart run <nameofyourdartfile>

Reading user input

We can read the input provided by the use with the help of the standard input class (stdin) that is available to us in the 'dart:io' library.

Example

Consider the example shown below −

 Live Demo

import 'dart:io';

void main(List<String> arguments){
   stdout.write("What is your name?\r
");
   var name = stdin.readLineSync();
   print(name);
}

In the above code example, we are trying to write the string "What is your name?" to the console, and then later we are asking for user input and storing that input in the name variable and then finally we are printing that variable.

Output

What is your name?
mukul
mukul

It should be noted that there might be a case when the user doesn't enter anything and to handle that case we need to check if the user entered nothing, we can do that by making use of the null aware operators that dart provides us.

Example

Consider the example shown below −

import 'dart:io';

void main(List<String> arguments){
   stdout.write("What is your name?\r
");
   var name;
   name = name ?? stdin.readLineSync();
   name.isEmpty ? stdout.write('Enter a name
') : stdout.write('Welcome ${name}
');
}

In the above code example, if we encounter a case where the user entered nothing we can simply return a standard message to the terminal, saying 'Enter a name'.

Output

What is your name?

Enter a name