macro_rules! writeln {
($dst:expr) => { ... };
($dst:expr,) => { ... };
($dst: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, Result};
fn main() -> Result<()> {
let mut w = Vec::new();
writeln!(&mut w)?;
writeln!(&mut w, "test")?;
writeln!(&mut w, "formatted {}", "arguments")?;
assert_eq!(&w[..], "\ntest\nformatted arguments\n".as_bytes());
Ok(())
}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;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let mut s = String::new();
let mut v = Vec::new();
writeln!(&mut s, "{} {}", "abc", 123)?; // uses fmt::Write::write_fmt
writeln!(&mut v, "s = {:?}", s)?; // uses io::Write::write_fmt
assert_eq!(v, b"s = \"abc 123\\n\"\n");
Ok(())
}
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/macro.writeln.html