Error handling best practices in Rust - Mini Project: Build & Apply

Error handling best practices

📖 Scenario: You are building a simple Rust program that reads a username from a file and prints a greeting. Handling errors properly is important to make your program reliable and user-friendly.

🎯 Goal: Learn how to handle errors in Rust using Result, match, and the ? operator to write clean and safe code.

📋 What You'll Learn

Create a function to read a username from a file

Use a configuration variable for the filename

Handle errors using match and Result

Use the ? operator for error propagation

Print the greeting or an error message

💡 Why This Matters

🌍 Real World

Reading configuration or user data from files is common in many programs. Handling errors properly prevents crashes and helps users understand what went wrong.

💼 Career

Rust developers must write safe and reliable code. Understanding error handling with Result, match, and the ? operator is essential for building robust applications.

1

DATA SETUP: Create a function to read username from a file

Write a function called read_username that returns a Result. Inside, use std::fs::read_to_string to read from a file named "user.txt" and return the content.

Rust

fn read_username() -> Result {
    // Your code here
}

Hint

Use std::fs::read_to_string("user.txt") to read the file content and return it directly.

2

CONFIGURATION: Add a variable for the filename

Create a variable called filename and set it to "user.txt". Update the read_username function to use this filename variable instead of the hardcoded string.

Rust

const filename: &str = "user.txt";

fn read_username() -> Result {
    // Your code here
}

Hint

Define filename outside the function and use it inside read_username.

3

CORE LOGIC: Use match to handle errors when calling read_username

Call read_username() and use a match statement with variables username and error to handle the Ok and Err cases. In Ok, print "Hello, {username}!". In Err, print "Failed to read username: {error}".

Rust

fn main() {
    let result = read_username();

    // Your code here
}

Hint

Use match result with Ok(username) and Err(error) arms to print messages.

4

OUTPUT: Use the ? operator in read_username and print the greeting in main

Rewrite read_username to use the ? operator for error propagation. Then, in main, call read_username() and use match with variables username and error to print "Hello, {username}!" or "Failed to read username: {error}".

Rust

fn read_username() -> Result {
    // Your code here
}

fn main() {
    // Your code here
}

Hint

Use ? operator inside read_username to return errors quickly. Then handle the result in main with match.

Make sure the file user.txt contains Alice for testing.