Vector, u8 strings

Suppose we have a byte vector (with u8 elements) in Rust. We want to append strings as byte data to the vector.

With a helper method, we can loop over strings (or other kinds of arguments) and push u8 elements. We must pass the vector as a mutable reference.

Example program

To begin, we introduce the append_string function. This receives 2 parameters: the mutable vector, and the string data we want to append.

fn append_string(buffer: &mut Vec<u8>, data: &str) {
    // Get bytes from string, and push them to the vector.
    for value in data.bytes() {
        buffer.push(value);
    }
}

fn main() {
    // Create a new vector, and append bytes from 3 strings to it.
    let mut buffer = Vec::new();
    append_string(&mut buffer, "soft");
    append_string(&mut buffer, " orange");
    append_string(&mut buffer, " cat");
    // Print result as string from vector.
    let result = String::from_utf8(buffer).unwrap();
    println!("RESULT: {:?}", result)
}
RESULT: "soft orange cat"

Notes, mut keyword

When we use the "mut" keyword to pass an argument, this indicates the function modifies the argument somehow. In append_string, the push() call modifies the buffer.

Extend from slice

There is a faster way to push bytes from a slice to a Vector. We can use the extend_from_slice function instead of a for-loop with push.

We built a helpful method that appends data from a string argument to a Vector of bytes. It loops over the strings, and appends the bytes.