Macro core::writeln1.0.0[][src]

macro_rules! writeln {
    ($dst:expr) => { ... };
    ($dst:expr,) => { ... };
    ($dst:expr, $fmt:expr) => { ... };
    ($dst:expr, $fmt:expr, $($arg:tt)*) => { ... };

Write formatted data into a buffer, with a newline appended.

On all platforms, the newline is the LINE FEED character (\n/U+000A) alone (no additional CARRIAGE RETURN (\r/U+000D).

For more information, see write!. For information on the format string syntax, see std::fmt.


use std::io::Write;

let mut w = Vec::new();
writeln!(&mut w).unwrap();
writeln!(&mut w, "test").unwrap();
writeln!(&mut w, "formatted {}", "arguments").unwrap();

assert_eq!(&w[..], "\ntest\nformatted arguments\n".as_bytes());Run

A module can import both std::fmt::Write and std::io::Write and call write! on objects implementing either, as objects do not typically implement both. However, the module must import the traits qualified so their names do not conflict:

use std::fmt::Write as FmtWrite;
use std::io::Write as IoWrite;

let mut s = String::new();
let mut v = Vec::new();
writeln!(&mut s, "{} {}", "abc", 123).unwrap(); // uses fmt::Write::write_fmt
writeln!(&mut v, "s = {:?}", s).unwrap(); // uses io::Write::write_fmt
assert_eq!(v, b"s = \"abc 123\\n\"\n");Run