Home » Rust » Rust Programs

Rust program to append data into an existing file

Rust | File I/O Example: Write a program to append data into an existing file.
Submitted by Nidhi, on October 30, 2021

Problem Solution:

In this program, we will open an existing file in append mode and write text data into the file using the write_all() method, and print the appropriate message.

Program/Source Code:

The source code to append data into the existing file is given below. The given program is compiled and executed on UBUNTU 18.04 successfully.

// Rust program to append data into existing file

use std::fs::OpenOptions;
use std::io::Write;

fn main() {
    let mut fileRef = OpenOptions::new().append(true).open("sample.txt").expect("Unable to open file");   
    
    fileRef.write_all("www.includehelp.com\n".as_bytes()).expect("write failed");
    println!("Data appended successfully");
}

Output:

$ rustc main.rs

$ ./main
Data appended successfully

$ cat sample.txt 
Hello World
Hello India
www.includehelp.com

Explanation:

In the main() function, we opened an existing file "sample.txt" in append mode. Then we wrote text data into the file using the write_all() method and printed file data.