Write in alloc::fmt - Rust
Description: A trait for writing or formatting into Unicode-accepting buffers or streams.

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## Write

# Trait Write

1.36.0 · Source

    pub trait Write {
        // Required method
        fn write_str(&mut self, s: &str) -> Result<(), Error>;

        // Provided methods
        fn write_char(&mut self, c: char) -> Result<(), Error> { ... }
        fn write_fmt(&mut self, args: Arguments<'_>) -> Result<(), Error> { ... }
    }

Expand description

A trait for writing or formatting into Unicode-accepting buffers or streams.

This trait only accepts UTF-8–encoded data and is not flushable. If you only want to accept Unicode and you don’t need flushing, you should implement this trait; otherwise you should implement `std::io::Write`.

## Required Methods§

1.0.0 · Source

#### fn write_str(&mut self, s: &str) -> Result<(), Error>

Writes a string slice into this writer, returning whether the write succeeded.

This method can only succeed if the entire string slice was successfully written, and this method will not return until all data has been written or an error occurs.

##### §Errors

This function will return an instance of `std::fmt::Error` on error.

The purpose of that error is to abort the formatting operation when the underlying destination encounters some error preventing it from accepting more text; in particular, it does not communicate any information about what error occurred. It should generally be propagated rather than handled, at least when implementing formatting traits.

##### §Examples

    use std::fmt::{Error, Write};

    fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
        f.write_str(s)
    }

    let mut buf = String::new();
    writer(&mut buf, "hola")?;
    assert_eq!(&buf, "hola");

## Provided Methods§

1.1.0 · Source

#### fn write_char(&mut self, c: char) -> Result<(), Error>

Writes a `char` into this writer, returning whether the write succeeded.

A single `char` may be encoded as more than one byte. This method can only succeed if the entire byte sequence was successfully written, and this method will not return until all data has been written or an error occurs.

##### §Errors

This function will return an instance of `Error` on error.

##### §Examples

    use std::fmt::{Error, Write};

    fn writer<W: Write>(f: &mut W, c: char) -> Result<(), Error> {
        f.write_char(c)
    }

    let mut buf = String::new();
    writer(&mut buf, 'a')?;
    writer(&mut buf, 'b')?;
    assert_eq!(&buf, "ab");

1.0.0 · Source

#### fn write_fmt(&mut self, args: Arguments<'_>) -> Result<(), Error>

Glue for usage of the `write!` macro with implementors of this trait.

This method should generally not be invoked manually, but rather through the `write!` macro itself.

##### §Errors

This function will return an instance of `Error` on error. Please see write_str for details.

##### §Examples

    use std::fmt::{Error, Write};

    fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
        f.write_fmt(format_args!("{s}"))
    }

    let mut buf = String::new();
    writer(&mut buf, "world")?;
    assert_eq!(&buf, "world");

## Implementors§

1.0.0 · Source§

### impl Write for String

1.2.0 · Source§

### impl Write for Formatter<'_>

1.4.0 · Source§

### impl<W> Write for &mut W
where W: Write + ?Sized,