cfg

Conditional compilation is possible through two different operators:

  • the cfg attribute: #[cfg(...)] in attribute position
  • the cfg! macro: cfg!(...) in boolean expressions

Both utilize identical argument syntax.

  1. // This function only gets compiled if the target OS is linux
  2. #[cfg(target_os = "linux")]
  3. fn are_you_on_linux() {
  4.     println!("You are running linux!");
  5. }
  7. // And this function only gets compiled if the target OS is *not* linux
  8. #[cfg(not(target_os = "linux"))]
  9. fn are_you_on_linux() {
  10.     println!("You are *not* running linux!");
  11. }
  13. fn main() {
  14.     are_you_on_linux();
  16.     println!("Are you sure?");
  17.     if cfg!(target_os = "linux") {
  18.         println!("Yes. It's definitely linux!");
  19.     } else {
  20.         println!("Yes. It's definitely *not* linux!");
  21.     }
  22. }

See also:

the reference, cfg!, and macros.