Rust Date Parser: Handling user input and Parsing errors

Last update on June 10 2025 07:12:34 (UTC/GMT +8 hours)

Write a Rust program that accepts user input for a date, parses it, and prints it in a different format, handling parsing errors.

Sample Solution:

Rust Code:

use std::io;

fn main() {
    println!("Please enter a date in the format YYYY-MM-DD:");
    
    let mut input = String::new();
    io::stdin().read_line(&mut input).expect("Failed to read input.");
    
    // Trim any leading or trailing whitespace from the input
    let trimmed_input = input.trim();
    
    // Attempt to parse the input date
    match parse_date(trimmed_input) {
        Ok(parsed_date) => println!("Parsed date: {}", parsed_date),
        Err(err) => eprintln!("Error parsing date: {}", err),
    }
}

fn parse_date(date_str: &str) -> Result<String, &str> {
    // Attempt to split the date string into its components
    let parts: Vec<&str> = date_str.split('-').collect();
    
    // Check if the date string has three components
    if parts.len() != 3 {
        return Err("Invalid date format. Please use YYYY-MM-DD.");
    }
    
    // Attempt to parse the components into integers
    let year: i32 = match parts[0].parse() {
        Ok(year) => year,
        Err(_) => return Err("Invalid year."),
    };
    
    let month: u32 = match parts[1].parse() {
        Ok(month) if (1..=12).contains(&month) => month,
        _ => return Err("Invalid month."),
    };
    
    let day: u32 = match parts[2].parse() {
        Ok(day) if (1..=31).contains(&day) => day,
        _ => return Err("Invalid day."),
    };
    
    // Format the parsed date components
    let parsed_date = format!("{}-{:02}-{:02}", year, month, day);
    
    Ok(parsed_date)
}

Output:

Please enter a date in the format YYYY-MM-DD: 2000-02-02
Parsed date: 2000-02-02

Please enter a date in the format YYYY-MM-DD: 2001-13-12
   Compiling playground v0.0.1 (/playground)
    Finished dev [unoptimized + debuginfo] target(s) in 0.65s
     Running `target/debug/playground`
Error parsing date: Invalid month.

Please enter a date in the format YYYY-MM-DD: 2001-02-32
  Compiling playground v0.0.1 (/playground)
    Finished dev [unoptimized + debuginfo] target(s) in 0.58s
     Running `target/debug/playground`
Error parsing date: Invalid day.

Explanation:

Here's a brief explanation of the above Rust code:

The main function:

Prints a message asking the user to enter a date.
Reads the user input from the console.
Trims any leading or trailing whitespace from the input.
Calls the "parse_date()" function to attempt to parse the input date.
Prints either the parsed date or an error message depending on the result of the parsing.

The parse_date function:

Attempts to split the input date string into its components (year, month, day) based on the '-' delimiter.
Checks if the date string has exactly three components. If not, it returns an error indicating an invalid date format.
Attempts to parse each component into integers (year, month, day).
Validates the parsed year, month, and day:

For the year, it checks if it can be parsed into an integer.
For the month, it checks if it falls within the range of 1 to 12 (inclusive).
For the day, it checks if it falls within the range 1 to 31 (inclusive).

If any parsing or validation fails, it returns an error with an appropriate error message.
If parsing and validation succeed, it formats the parsed date components into the YYYY-MM-DD format and returns it as a "String".

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