Trait std::io::Write [−] [src]

pub trait Write {
    fn write(&mut self, buf: &[u8]) -> Result<usize>;
    fn flush(&mut self) -> Result<()>;

    fn write_all(&mut self, buf: &[u8]) -> Result<()> { ... }
    fn write_fmt(&mut self, fmt: Arguments) -> Result<()> { ... }
    fn by_ref(&mut self) -> &mut Self where Self: Sized { ... }
    fn broadcast<W: Write>(self, other: W) -> Broadcast<Self, W> where Self: Sized { ... }
}

A trait for objects which are byte-oriented sinks.

Implementors of the Write trait are sometimes called 'writers'.

Writers are defined by two required methods, write() and flush():

Writers are intended to be composable with one another. Many implementors throughout std::io take and provide types which implement the Write trait.

Examples

fn main() { use std::io::prelude::*; use std::fs::File; fn foo() -> std::io::Result<()> { let mut buffer = try!(File::create("foo.txt")); try!(buffer.write(b"some bytes")); Ok(()) } }
use std::io::prelude::*;
use std::fs::File;

let mut buffer = try!(File::create("foo.txt"));

try!(buffer.write(b"some bytes"));

Required Methods

fn write(&mut self, buf: &[u8]) -> Result<usize>

Write a buffer into this object, returning how many bytes were written.

This function will attempt to write the entire contents of buf, but the entire write may not succeed, or the write may also generate an error. A call to write represents at most one attempt to write to any wrapped object.

Calls to write are not guaranteed to block waiting for data to be written, and a write which would otherwise block can be indicated through an Err variant.

If the return value is Ok(n) then it must be guaranteed that 0 <= n <= buf.len(). A return value of 0 typically means that the underlying object is no longer able to accept bytes and will likely not be able to in the future as well, or that the buffer provided is empty.

Errors

Each call to write may generate an I/O error indicating that the operation could not be completed. If an error is returned then no bytes in the buffer were written to this writer.

It is not considered an error if the entire buffer could not be written to this writer.

Examples

fn main() { use std::io::prelude::*; use std::fs::File; fn foo() -> std::io::Result<()> { let mut buffer = try!(File::create("foo.txt")); try!(buffer.write(b"some bytes")); Ok(()) } }
use std::io::prelude::*;
use std::fs::File;

let mut buffer = try!(File::create("foo.txt"));

try!(buffer.write(b"some bytes"));

fn flush(&mut self) -> Result<()>

Flush this output stream, ensuring that all intermediately buffered contents reach their destination.

Errors

It is considered an error if not all bytes could be written due to I/O errors or EOF being reached.

Examples

fn main() { use std::io::prelude::*; use std::io::BufWriter; use std::fs::File; fn foo() -> std::io::Result<()> { let mut buffer = BufWriter::new(try!(File::create("foo.txt"))); try!(buffer.write(b"some bytes")); try!(buffer.flush()); Ok(()) } }
use std::io::prelude::*;
use std::io::BufWriter;
use std::fs::File;

let mut buffer = BufWriter::new(try!(File::create("foo.txt")));

try!(buffer.write(b"some bytes"));
try!(buffer.flush());

Provided Methods

fn write_all(&mut self, buf: &[u8]) -> Result<()>

Attempts to write an entire buffer into this write.

This method will continuously call write while there is more data to write. This method will not return until the entire buffer has been successfully written or an error occurs. The first error generated from this method will be returned.

Errors

This function will return the first error that write returns.

Examples

fn main() { use std::io::prelude::*; use std::fs::File; fn foo() -> std::io::Result<()> { let mut buffer = try!(File::create("foo.txt")); try!(buffer.write_all(b"some bytes")); Ok(()) } }
use std::io::prelude::*;
use std::fs::File;

let mut buffer = try!(File::create("foo.txt"));

try!(buffer.write_all(b"some bytes"));

fn write_fmt(&mut self, fmt: Arguments) -> Result<()>

Writes a formatted string into this writer, returning any error encountered.

This method is primarily used to interface with the format_args! macro, but it is rare that this should explicitly be called. The write! macro should be favored to invoke this method instead.

This function internally uses the write_all method on this trait and hence will continuously write data so long as no errors are received. This also means that partial writes are not indicated in this signature.

Errors

This function will return any I/O error reported while formatting.

Examples

fn main() { use std::io::prelude::*; use std::fs::File; fn foo() -> std::io::Result<()> { let mut buffer = try!(File::create("foo.txt")); // this call try!(write!(buffer, "{:.*}", 2, 1.234567)); // turns into this: try!(buffer.write_fmt(format_args!("{:.*}", 2, 1.234567))); Ok(()) } }
use std::io::prelude::*;
use std::fs::File;

let mut buffer = try!(File::create("foo.txt"));

// this call
try!(write!(buffer, "{:.*}", 2, 1.234567));
// turns into this:
try!(buffer.write_fmt(format_args!("{:.*}", 2, 1.234567)));

fn by_ref(&mut self) -> &mut Self where Self: Sized

Creates a "by reference" adaptor for this instance of Write.

The returned adaptor also implements Write and will simply borrow this current writer.

Examples

fn main() { use std::io::Write; use std::fs::File; fn foo() -> std::io::Result<()> { let mut buffer = try!(File::create("foo.txt")); let reference = buffer.by_ref(); // we can use reference just like our original buffer try!(reference.write_all(b"some bytes")); Ok(()) } }
use std::io::Write;
use std::fs::File;

let mut buffer = try!(File::create("foo.txt"));

let reference = buffer.by_ref();

// we can use reference just like our original buffer
try!(reference.write_all(b"some bytes"));

fn broadcast<W: Write>(self, other: W) -> Broadcast<Self, W> where Self: Sized

Deprecated since 1.6.0

: error handling semantics unclear and don't seem to have an ergonomic resolution

Creates a new writer which will write all data to both this writer and another writer.

All data written to the returned writer will both be written to self as well as other. Note that the error semantics of the current implementation do not precisely track where errors happen. For example an error on the second call to write will not report that the first call to write succeeded.

Examples

#![feature(io)] fn main() { use std::io::prelude::*; use std::fs::File; fn foo() -> std::io::Result<()> { let mut buffer1 = try!(File::create("foo.txt")); let mut buffer2 = Vec::new(); // write the output to buffer1 as we read let mut handle = buffer1.broadcast(&mut buffer2); try!(handle.write(b"some bytes")); Ok(()) } }
#![feature(io)]
use std::io::prelude::*;
use std::fs::File;

let mut buffer1 = try!(File::create("foo.txt"));
let mut buffer2 = Vec::new();

// write the output to buffer1 as we read
let mut handle = buffer1.broadcast(&mut buffer2);

try!(handle.write(b"some bytes"));

Implementors