Struct std::fs::File

pub struct File {
    // some fields omitted
}

A reference to an open file on the filesystem.

An instance of a File can be read and/or written depending on what options it was opened with. Files also implement Seek to alter the logical cursor that the file contains internally.

Examples

fn main() { use std::io::prelude::*; use std::fs::File; fn foo() -> std::io::Result<()> { let mut f = try!(File::create("foo.txt")); try!(f.write_all(b"Hello, world!")); let mut f = try!(File::open("foo.txt")); let mut s = String::new(); try!(f.read_to_string(&mut s)); assert_eq!(s, "Hello, world!"); Ok(()) } }

use std::io::prelude::*;
use std::fs::File;

let mut f = try!(File::create("foo.txt"));
try!(f.write_all(b"Hello, world!"));

let mut f = try!(File::open("foo.txt"));
let mut s = String::new();
try!(f.read_to_string(&mut s));
assert_eq!(s, "Hello, world!");

Methods

impl File

fn open<P: AsRef<Path>>(path: P) -> Result<File>

Attempts to open a file in read-only mode.

See the OpenOptions::open method for more details.

Errors

This function will return an error if path does not already exist. Other errors may also be returned according to OpenOptions::open.

Examples

fn main() { use std::fs::File; fn foo() -> std::io::Result<()> { let mut f = try!(File::open("foo.txt")); Ok(()) } }

use std::fs::File;

let mut f = try!(File::open("foo.txt"));

fn create<P: AsRef<Path>>(path: P) -> Result<File>

Opens a file in write-only mode.

This function will create a file if it does not exist, and will truncate it if it does.

See the OpenOptions::open function for more details.

Examples

fn main() { use std::fs::File; fn foo() -> std::io::Result<()> { let mut f = try!(File::create("foo.txt")); Ok(()) } }

use std::fs::File;

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

fn sync_all(&self) -> Result<()>

Attempts to sync all OS-internal metadata to disk.

This function will attempt to ensure that all in-core data reaches the filesystem before returning.

Examples

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

use std::fs::File;
use std::io::prelude::*;

let mut f = try!(File::create("foo.txt"));
try!(f.write_all(b"Hello, world!"));

try!(f.sync_all());

fn sync_data(&self) -> Result<()>

This function is similar to sync_all, except that it may not synchronize file metadata to the filesystem.

This is intended for use cases that must synchronize content, but don't need the metadata on disk. The goal of this method is to reduce disk operations.

Note that some platforms may simply implement this in terms of sync_all.

Examples

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

use std::fs::File;
use std::io::prelude::*;

let mut f = try!(File::create("foo.txt"));
try!(f.write_all(b"Hello, world!"));

try!(f.sync_data());

fn set_len(&self, size: u64) -> Result<()>

Truncates or extends the underlying file, updating the size of this file to become size.

If the size is less than the current file's size, then the file will be shrunk. If it is greater than the current file's size, then the file will be extended to size and have all of the intermediate data filled in with 0s.

Errors

This function will return an error if the file is not opened for writing.

Examples

fn main() { use std::fs::File; fn foo() -> std::io::Result<()> { let mut f = try!(File::create("foo.txt")); try!(f.set_len(10)); Ok(()) } }

use std::fs::File;

let mut f = try!(File::create("foo.txt"));
try!(f.set_len(10));

fn metadata(&self) -> Result<Metadata>

Queries metadata about the underlying file.

Examples

fn main() { use std::fs::File; fn foo() -> std::io::Result<()> { let mut f = try!(File::open("foo.txt")); let metadata = try!(f.metadata()); Ok(()) } }

use std::fs::File;

let mut f = try!(File::open("foo.txt"));
let metadata = try!(f.metadata());

fn try_clone(&self) -> Result<File>

Creates a new independently owned handle to the underlying file.

The returned File is a reference to the same state that this object references. Both handles will read and write with the same cursor position.

Trait Implementations

impl Debug for File

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Read for File

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

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>

Read all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize>

Read all bytes until EOF in this source, placing them into buf.

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

Read the exact number of bytes required to fill buf.

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

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

fn bytes(self) -> Bytes<Self> where Self: Sized

Transforms this Read instance to an Iterator over its bytes.

fn chars(self) -> Chars<Self> where Self: Sized

Transforms this Read instance to an Iterator over chars.

fn chain<R: Read>(self, next: R) -> Chain<Self, R> where Self: Sized

Creates an adaptor which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self> where Self: Sized

Creates an adaptor which will read at most limit bytes from it.

impl Write for File

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

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

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

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

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

Attempts to write an entire buffer into this write.

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

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

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

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

impl Seek for File

fn seek(&mut self, pos: SeekFrom) -> Result<u64>

Seek to an offset, in bytes, in a stream.

impl<'a> Read for &'a File

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

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>

Read all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize>

Read all bytes until EOF in this source, placing them into buf.

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

Read the exact number of bytes required to fill buf.

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

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

fn bytes(self) -> Bytes<Self> where Self: Sized

Transforms this Read instance to an Iterator over its bytes.

fn chars(self) -> Chars<Self> where Self: Sized

Transforms this Read instance to an Iterator over chars.

fn chain<R: Read>(self, next: R) -> Chain<Self, R> where Self: Sized

Creates an adaptor which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self> where Self: Sized

Creates an adaptor which will read at most limit bytes from it.

impl<'a> Write for &'a File

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

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

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

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

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

Attempts to write an entire buffer into this write.

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

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

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

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

impl<'a> Seek for &'a File

fn seek(&mut self, pos: SeekFrom) -> Result<u64>

Seek to an offset, in bytes, in a stream.

impl AsRawFd for File

fn as_raw_fd(&self) -> RawFd

Extracts the raw file descriptor.

impl FromRawFd for File

unsafe fn from_raw_fd(fd: RawFd) -> File

Constructs a new instances of Self from the given raw file descriptor.

impl IntoRawFd for File

fn into_raw_fd(self) -> RawFd

Consumes this object, returning the raw underlying file descriptor.