#[windows_subsystem = "..."]Attribute

Explanation

#![windows_subsystem = "..."] is an inner attribute placed at the top of a crate root that selects which Windows PE subsystem the compiled executable is linked as. It is meaningful only when compiling for a Windows target; on every other target it has no effect at all.

Windows executables declare, in their binary header, which of two subsystems they belong to. "console" is the default: the OS automatically attaches a console window to the process if it wasn't already launched from one, which is the right behavior for a command-line tool. "windows" marks the executable as a GUI application: launching it does not open a console window, which is what any ordinary graphical desktop application wants — a windowed app popping up a blank black console alongside its actual window looks broken to a user.

This attribute exists purely to control that one piece of platform metadata; it does not change how the program compiles, what APIs are available, or anything about std's own behavior. Note the practical consequence of choosing "windows": println!/eprintln! output has nowhere visible to go, since there is no attached console to write to — a GUI application generally needs its own logging or message-box-based error reporting instead of relying on standard output.

Usage examples

#![windows_subsystem = "windows"] // <- Windows-only: suppresses the console window at launch

fn main() {
    // a real GUI application would open its window here instead
}

#![cfg_attr(windows, windows_subsystem = "windows")] // <- applies only when actually targeting Windows

fn main() {
    // launch the application's GUI window here
}