How to read and write files in Rust

File input/output operations are essential for working with data stored in files. In Rust, reading and writing files involves utilizing the std::fs::File struct and other related types. This Answer provides a step-by-step approach to reading and writing files, error handling, and working with file metadata.

Syntax

For reading a file in Rust, the following syntax is typically used:

//Necessary imports
use std::fs::File;
use std::fs::OpenOptions;
use std::io::{Write, BufReader, BufRead, Error};
fn main() -> Result<(), Error> {
    let path = "output/example.txt";
    // creating 
    let mut open = File::create(path)?;
    // writing to file
    write!(open, "Hello World!\n")?;
    
    // reading
    println!("{}", "First read:");
    let open = File::open(path)?;
    let reader = BufReader::new(open);
    for x in reader.lines() {
        println!("{}", x?);
    }
    // writing to an existing file
    let mut open = OpenOptions::new().append(true).open(path).expect("Unable to open file");   
    open.write_all("Again Hello World!\n".as_bytes()).expect("write failed");
    // reading
    println!("{}", "Second read:");
    let open = File::open(path)?;
    let reader = BufReader::new(open);
    for x in reader.lines() {
        println!("{}", x?);
    }
    Ok(())
}

Note: To view the output of the code above, press the arrow at the right.

Explanation

The code above is explained in detail below:

Lines 2–4: We import the necessary modules and types from the standard library.
Line 7: We initialize the path variable with the path of the file.
Line 9: The File::create(path)? creates a new file at the specified path and returns a File object. The ? operator is used to propagate any potential error that occurs during file creation.
Line 11: We use the write() function to write into our file.
Lines 15–20: We read the newly created file.
Lines 22–23: Here, we update the file using OpenOptions::new().append(true).open(path) that opens the file in the append mode and returns a mutable File object.
Lines 26–31: We read the file again.

Conclusion

Reading and writing files in Rust is a fundamental aspect of file I/O operations. We can perform efficient and reliable file operations by utilizing the struct, along with other related types and functions.

How to read and write files in Rust

Syntax

Implementation

Explanation

Conclusion