print!

The print! macro writes formatted text to the standard output stream (stdout) without appending a trailing newline (\n).

Buffering Behavior and Explicit flush()

By default, standard output (io::stdout()) in Rust is line-buffered when connected to an interactive terminal: bytes buffered by print! are held in memory until a \n character is written, the internal buffer fills up, or io::stdout().flush() is called explicitly.

When displaying an interactive prompt (print!("Enter username: ");) or a single-line progress indicator before blocking on input or work, always call io::stdout().flush() so the text appears on screen immediately:

use std::io::{self, Write};

fn main() -> io::Result<()> {
    print!("Loading modules: ");
    io::stdout().flush()?; // Forces buffered prompt to appear immediately

    for module in ["core", "net", "storage"] {
        print!("[{module}] ");
        io::stdout().flush()?;
    }
    println!("done.");
    Ok(())
}

Loading modules: [core] [net] [storage] done.

Building Tables or Grids Row by Row with print! and println!

Combining print! for cells across a row with println!() at the end of each row formats 2D tables cleanly without allocating intermediate row strings:

fn main() {
    for row in 1..=3 {
        for col in 1..=4 {
            print!("{:>4}", row * col);
        }
        println!(); // Terminates the current row
    }
}

   1   2   3   4
   2   4   6   8
   3   6   9  12

print! vs. println!