1.0.0[][src]Struct std::fs::File

pub struct File { /* 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.

Files are automatically closed when they go out of scope.

Examples

Creates a new file and write bytes to it:

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

fn main() -> std::io::Result<()> {
    let mut file = File::create("foo.txt")?;
    file.write_all(b"Hello, world!")?;
    Ok(())
}Run

Read the contents of a file into a String:

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

fn main() -> std::io::Result<()> {
    let mut file = File::open("foo.txt")?;
    let mut contents = String::new();
    file.read_to_string(&mut contents)?;
    assert_eq!(contents, "Hello, world!");
    Ok(())
}Run

It can be more efficient to read the contents of a file with a buffered Reader. This can be accomplished with BufReader<R>:

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

fn main() -> std::io::Result<()> {
    let file = File::open("foo.txt")?;
    let mut buf_reader = BufReader::new(file);
    let mut contents = String::new();
    buf_reader.read_to_string(&mut contents)?;
    assert_eq!(contents, "Hello, world!");
    Ok(())
}Run

Note that, although read and write methods require a &mut File, because of the interfaces for Read and Write, the holder of a &File can still modify the file, either through methods that take &File or by retrieving the underlying OS object and modifying the file that way. Additionally, many operating systems allow concurrent modification of files by different processes. Avoid assuming that holding a &File means that the file will not change.

Methods

impl File[src]

pub fn open<P: AsRef<Path>>(path: P) -> Result<File>[src]

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

use std::fs::File;

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

pub fn create<P: AsRef<Path>>(path: P) -> Result<File>[src]

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

use std::fs::File;

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

pub fn sync_all(&self) -> Result<()>[src]

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

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

fn main() -> std::io::Result<()> {
    let mut f = File::create("foo.txt")?;
    f.write_all(b"Hello, world!")?;

    f.sync_all()?;
    Ok(())
}Run

pub fn sync_data(&self) -> Result<()>[src]

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

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

fn main() -> std::io::Result<()> {
    let mut f = File::create("foo.txt")?;
    f.write_all(b"Hello, world!")?;

    f.sync_data()?;
    Ok(())
}Run

pub fn set_len(&self, size: u64) -> Result<()>[src]

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.

The file's cursor isn't changed. In particular, if the cursor was at the end and the file is shrunk using this operation, the cursor will now be past the end.

Errors

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

Examples

use std::fs::File;

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

Note that this method alters the content of the underlying file, even though it takes &self rather than &mut self.

pub fn metadata(&self) -> Result<Metadata>[src]

Queries metadata about the underlying file.

Examples

use std::fs::File;

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

pub fn try_clone(&self) -> Result<File>
1.9.0
[src]

Creates a new File instance that shares the same underlying file handle as the existing File instance. Reads, writes, and seeks will affect both File instances simultaneously.

Examples

Creates two handles for a file named foo.txt:

use std::fs::File;

fn main() -> std::io::Result<()> {
    let mut file = File::open("foo.txt")?;
    let file_copy = file.try_clone()?;
    Ok(())
}Run

Assuming there’s a file named foo.txt with contents abcdef\n, create two handles, seek one of them, and read the remaining bytes from the other handle:

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

fn main() -> std::io::Result<()> {
    let mut file = File::open("foo.txt")?;
    let mut file_copy = file.try_clone()?;

    file.seek(SeekFrom::Start(3))?;

    let mut contents = vec![];
    file_copy.read_to_end(&mut contents)?;
    assert_eq!(contents, b"def\n");
    Ok(())
}Run

pub fn set_permissions(&self, perm: Permissions) -> Result<()>
1.16.0
[src]

Changes the permissions on the underlying file.

Platform-specific behavior

This function currently corresponds to the fchmod function on Unix and the SetFileInformationByHandle function on Windows. Note that, this may change in the future.

Errors

This function will return an error if the user lacks permission change attributes on the underlying file. It may also return an error in other os-specific unspecified cases.

Examples

fn main() -> std::io::Result<()> {
    use std::fs::File;

    let file = File::open("foo.txt")?;
    let mut perms = file.metadata()?.permissions();
    perms.set_readonly(true);
    file.set_permissions(perms)?;
    Ok(())
}Run

Note that this method alters the permissions of the underlying file, even though it takes &self rather than &mut self.

Trait Implementations

impl Read for File[src]

fn read_vectored(&mut self, bufs: &mut [IoVecMut]) -> Result<usize>[src]

🔬 This is a nightly-only experimental API. (iovec #58452)

Like read, except that it reads into a slice of buffers. Read more

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

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

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

Read all bytes until EOF in this source, appending them to buf. Read more

fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
1.6.0
[src]

Read the exact number of bytes required to fill buf. Read more

Important traits for &'_ mut I
fn by_ref(&mut self) -> &mut Self where
    Self: Sized
[src]

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

Important traits for Bytes<R>
fn bytes(self) -> Bytes<Self> where
    Self: Sized
[src]

Transforms this Read instance to an [Iterator] over its bytes. Read more

Important traits for Chain<T, U>
fn chain<R: Read>(self, next: R) -> Chain<Self, R> where
    Self: Sized
[src]

Creates an adaptor which will chain this stream with another. Read more

Important traits for Take<T>
fn take(self, limit: u64) -> Take<Self> where
    Self: Sized
[src]

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

impl<'_> Read for &'_ File[src]

fn read_vectored(&mut self, bufs: &mut [IoVecMut]) -> Result<usize>[src]

🔬 This is a nightly-only experimental API. (iovec #58452)

Like read, except that it reads into a slice of buffers. Read more

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

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

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

Read all bytes until EOF in this source, appending them to buf. Read more

fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
1.6.0
[src]

Read the exact number of bytes required to fill buf. Read more

Important traits for &'_ mut I
fn by_ref(&mut self) -> &mut Self where
    Self: Sized
[src]

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

Important traits for Bytes<R>
fn bytes(self) -> Bytes<Self> where
    Self: Sized
[src]

Transforms this Read instance to an [Iterator] over its bytes. Read more

Important traits for Chain<T, U>
fn chain<R: Read>(self, next: R) -> Chain<Self, R> where
    Self: Sized
[src]

Creates an adaptor which will chain this stream with another. Read more

Important traits for Take<T>
fn take(self, limit: u64) -> Take<Self> where
    Self: Sized
[src]

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

impl Write for File[src]

fn write_vectored(&mut self, bufs: &[IoVec]) -> Result<usize>[src]

🔬 This is a nightly-only experimental API. (iovec #58452)

Like write, except that it writes from a slice of buffers. Read more

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

Attempts to write an entire buffer into this writer. Read more

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

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

Important traits for &'_ mut I
fn by_ref(&mut self) -> &mut Self where
    Self: Sized
[src]

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

impl<'_> Write for &'_ File[src]

fn write_vectored(&mut self, bufs: &[IoVec]) -> Result<usize>[src]

🔬 This is a nightly-only experimental API. (iovec #58452)

Like write, except that it writes from a slice of buffers. Read more

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

Attempts to write an entire buffer into this writer. Read more

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

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

Important traits for &'_ mut I
fn by_ref(&mut self) -> &mut Self where
    Self: Sized
[src]

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

impl Seek for File[src]

fn stream_len(&mut self) -> Result<u64>[src]

🔬 This is a nightly-only experimental API. (seek_convenience #0)

Returns the length of this stream (in bytes). Read more

fn stream_position(&mut self) -> Result<u64>[src]

🔬 This is a nightly-only experimental API. (seek_convenience #0)

Returns the current seek position from the start of the stream. Read more

impl<'_> Seek for &'_ File[src]

fn stream_len(&mut self) -> Result<u64>[src]

🔬 This is a nightly-only experimental API. (seek_convenience #0)

Returns the length of this stream (in bytes). Read more

fn stream_position(&mut self) -> Result<u64>[src]

🔬 This is a nightly-only experimental API. (seek_convenience #0)

Returns the current seek position from the start of the stream. Read more

impl AsRawFd for File[src]

impl FromRawFd for File
1.1.0
[src]

impl IntoRawFd for File
1.4.0
[src]

impl FileExt for File
1.15.0
[src]

fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
1.33.0
[src]

This is supported on Unix only.

Reads the exact number of byte required to fill buf from the given offset. Read more

fn write_all_at(&self, buf: &[u8], offset: u64) -> Result<()>
1.33.0
[src]

This is supported on Unix only.

Attempts to write an entire buffer starting from a given offset. Read more

impl FileExt for File
1.15.0
[src]

impl AsRawHandle for File[src]

impl FromRawHandle for File
1.1.0
[src]

impl IntoRawHandle for File
1.4.0
[src]

impl Debug for File[src]

impl From<File> for Stdio
1.20.0
[src]

fn from(file: File) -> Stdio[src]

Converts a File into a Stdio

Examples

File will be converted to Stdio using Stdio::from under the hood.

use std::fs::File;
use std::process::Command;

// With the `foo.txt` file containing `Hello, world!"
let file = File::open("foo.txt").unwrap();

let reverse = Command::new("rev")
    .stdin(file)  // Implicit File conversion into a Stdio
    .output()
    .expect("failed reverse command");

assert_eq!(reverse.stdout, b"!dlrow ,olleH");Run

Auto Trait Implementations

impl Send for File

impl Sync for File

Blanket Implementations

impl<T> From for T[src]

impl<T, U> TryFrom for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T, U> Into for T where
    U: From<T>, 
[src]

impl<T> Borrow for T where
    T: ?Sized
[src]

impl<T> BorrowMut for T where
    T: ?Sized
[src]

impl<T> Any for T where
    T: 'static + ?Sized
[src]