Add eprint! and eprintln! macros to the prelude. by zackw · Pull Request #39229 · rust-lang/rust (original) (raw)
@@ -68,6 +68,9 @@ macro_rules! panic {
/// necessary to use `io::stdout().flush()` to ensure the output is emitted
/// immediately.
///
/// Use `print!` only for the primary output of your program. Use
/// `eprint!` instead to print error and progress messages.
///
/// # Panics
///
/// Panics if writing to `io::stdout()` fails.
@@ -105,6 +108,9 @@ macro_rules! print {
/// Use the `format!` syntax to write data to the standard output.
/// See `std::fmt` for more information.
///
/// Use `println!` only for the primary output of your program. Use
/// `eprintln!` instead to print error and progress messages.
///
/// # Panics
///
/// Panics if writing to `io::stdout()` fails.
@@ -124,6 +130,45 @@ macro_rules! println {
($fmt:expr, (((arg:tt)*) => (print!(concat!($fmt, "\n"), (((arg)*));
}
/// Macro for printing to the standard error.
///
/// Equivalent to the `print!` macro, except that output goes to
/// `io::stderr()` instead of `io::stdout()`. See `print!` for
/// example usage.
///
/// Use `eprint!` only for error and progress messages. Use `print!`
/// instead for the primary output of your program.
///
/// # Panics
///
/// Panics if writing to `io::stderr()` fails.
#[macro_export]
#[unstable(feature = "eprint", issue="39228")]
#[allow_internal_unstable]
macro_rules! eprint {
($($arg:tt)*) => ($crate::io::_eprint(format_args!($($arg)*)));
}
/// Macro for printing to the standard error, with a newline.
///
/// Equivalent to the `println!` macro, except that output goes to
/// `io::stderr()` instead of `io::stdout()`. See `println!` for
/// example usage.
///
/// Use `eprintln!` only for error and progress messages. Use `println!`
/// instead for the primary output of your program.
///
/// # Panics
///
/// Panics if writing to `io::stderr()` fails.
#[macro_export]
#[unstable(feature = "eprint", issue="39228")]
macro_rules! eprintln {
() => (eprint!("\n"));
($fmt:expr) => (eprint!(concat!($fmt, "\n")));
($fmt:expr, (((arg:tt)*) => (eprint!(concat!($fmt, "\n"), (((arg)*));
}
/// A macro to select an event from a number of receivers.
///
/// This macro is used to wait for the first event to occur on a number of