Table of contents📚
Reading a file📖
The use keyword
First, we need a file to read, so we will create a new file in our project folder.
# 📄 hello.txt
World, Hello 👋
Now, we will read the file and print its content.
First, we need to import the File struct from the std::fs module, which is the standard library for file handling.
To import a module, we use the use keyword.
use std::fs::File;
Then we need to import std::io::prelude::*; to allow us to perform read and write operations on the file.
use std::io::prelude::*;
The * means that we are importing all the methods from the prelude module.
The open and expect methods
The open method returns a Result type, which is a type that represents either a value or an error.
We can use the expect method to unwrap the Result type and get the value.
The value is a variable of type File.
The open method takes a path to the file as an argument.
let mut file = File::open("hello.txt").expect("Unable to open file");
The expect method is used to handle errors, if the file cannot be opened for any reason, the program will panic. For exemple if the file doesn’t exist, the program will print the error message and exit.
thread 'main' panicked at 'Failed to open hello.txt: Os { code: 2, kind: NotFound, message: "No such file or directory" }', rust.rs:5:41
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
The read_to_string method
the read_to_string takes a mutable reference to a String as an argument and returns a Result type. This function will read the entire file and store it in the String variable.
let mut content = String::new();
file.read_to_string(&mut content).expect("Unable to read file");
println!("📄 file content : {}", content);
Output:
📄 file content : World, Hello 👋