1.0.0[−][src]Macro core::write
Writes formatted data into a buffer.
This macro accepts a format string, a list of arguments, and a 'writer'. Arguments will be
formatted according to the specified format string and the result will be passed to the writer.
The writer may be any value with a write_fmt
method; generally this comes from an
implementation of either the std::fmt::Write
or the std::io::Write
trait. The macro
returns whatever the write_fmt
method returns; commonly a std::fmt::Result
, or an
io::Result
.
See std::fmt
for more information on the format string syntax.
Examples
use std::io::Write; let mut w = Vec::new(); write!(&mut w, "test").unwrap(); write!(&mut w, "formatted {}", "arguments").unwrap(); assert_eq!(w, b"testformatted arguments");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(); write!(&mut s, "{} {}", "abc", 123).unwrap(); // uses fmt::Write::write_fmt write!(&mut v, "s = {:?}", s).unwrap(); // uses io::Write::write_fmt assert_eq!(v, b"s = \"abc 123\"");Run
Note: This macro can be used in no_std
setups as well.
In a no_std
setup you are responsible for the implementation details of the components.
use core::fmt::Write; struct Example; impl Write for Example { fn write_str(&mut self, _s: &str) -> core::fmt::Result { unimplemented!(); } } let mut m = Example{}; write!(&mut m, "Hello World").expect("Not written");Run