The println! Macro

Basic Printing

The simplest use of println! takes a plain string literal and prints it followed by a newline. This is the very first thing most people write when learning Rust.

Example: Basic Printing

fn main() {
    println!("Simple text output");
}

Placeholders With {}

Curly braces {} act as placeholders inside the format string, filled in order by the extra arguments passed after the string. This lets you mix literal text with dynamic values in one call.

Note: Ferris is the unofficial mascot of Rust -- a friendly crab.

Example: Placeholders With {}

fn main() {
    let name = "Ferris";
    let age = 5;
    println!("{} is {} years old", name, age);
}

Named Arguments

You can name placeholders directly inside the braces, like {value}, and Rust matches them to named arguments passed after the format string, regardless of their position. This can make longer format strings easier to read.

Example: Named Arguments

fn main() {
    let city = "Berlin";
    let temp = 21;
    println!("It is {} degrees in {}", temp, city);
}

print! vs println!

print! behaves exactly like println! except it does not add a trailing newline. This means consecutive print! calls continue on the same line, which is useful for building output piece by piece.

Example: print! vs println!

fn main() {
    print!("No newline here... ");
    println!("but this one ends the line");
}