File in std::fs - Rust
Description: An object providing access to an open file on the filesystem.

## File

# Struct File

1.0.0 · Source

    pub struct File { /* private fields */ }

Expand description

An object providing access 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. Errors detected on closing are ignored by the implementation of `Drop`. Use the method `sync_all` if these errors must be manually handled.

`File` does not buffer reads and writes. For efficiency, consider wrapping the file in a `BufReader` or `BufWriter` when performing many small `read` or `write` calls, unless unbuffered reads and writes are required.

## §Examples

Creates a new file and write bytes to it (you can also use `write`):

    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(())
    }

Reads the contents of a file into a `String` (you can also use `read`):

    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(())
    }

Using a buffered `Read`er:

    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(())
    }

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.

## §Platform-specific behavior

On Windows, the implementation of `Read` and `Write` traits for `File` perform synchronous I/O operations. Therefore the underlying file must not have been opened for asynchronous I/O (e.g. by using `FILE_FLAG_OVERLAPPED`).

## Implementations§

Source§

### impl File

1.0.0 · Source

#### pub 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.

If you only need to read the entire file contents, consider `std::fs::read()` or `std::fs::read_to_string()` instead.

##### §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;
    use std::io::Read;

    fn main() -> std::io::Result<()> {
        let mut f = File::open("foo.txt")?;
        let mut data = vec![];
        f.read_to_end(&mut data)?;
        Ok(())
    }

Source

#### pub fn open_buffered<P: AsRef<Path>>(path: P) -> Result<BufReader<File>>

🔬This is a nightly-only experimental API. (`file_buffered` #130804)

Attempts to open a file in read-only mode with buffering.

See the `OpenOptions::open` method, the `BufReader` type, and the `BufRead` trait for more details.

If you only need to read the entire file contents, consider `std::fs::read()` or `std::fs::read_to_string()` instead.

##### §Errors

This function will return an error if `path` does not already exist, or if memory allocation fails for the new buffer. Other errors may also be returned according to `OpenOptions::open`.

##### §Examples

    #![feature(file_buffered)]
    use std::fs::File;
    use std::io::BufRead;

    fn main() -> std::io::Result<()> {
        let mut f = File::open_buffered("foo.txt")?;
        assert!(f.capacity() > 0);
        for (line, i) in f.lines().zip(1..) {
            println!("{i:6}: {}", line?);
        }
        Ok(())
    }

1.0.0 · Source

#### pub 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.

Depending on the platform, this function may fail if the full directory path does not exist. See the `OpenOptions::open` function for more details.

See also `std::fs::write()` for a simple function to create a file with some given data.

##### §Examples

    use std::fs::File;
    use std::io::Write;

    fn main() -> std::io::Result<()> {
        let mut f = File::create("foo.txt")?;
        f.write_all(&1234_u32.to_be_bytes())?;
        Ok(())
    }

Source

#### pub fn create_buffered<P: AsRef<Path>>(path: P) -> Result<BufWriter<File>>

🔬This is a nightly-only experimental API. (`file_buffered` #130804)

Opens a file in write-only mode with buffering.

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

Depending on the platform, this function may fail if the full directory path does not exist.

See the `OpenOptions::open` method and the `BufWriter` type for more details.

See also `std::fs::write()` for a simple function to create a file with some given data.

##### §Examples

    #![feature(file_buffered)]
    use std::fs::File;
    use std::io::Write;

    fn main() -> std::io::Result<()> {
        let mut f = File::create_buffered("foo.txt")?;
        assert!(f.capacity() > 0);
        for i in 0..100 {
            writeln!(&mut f, "{i}")?;
        }
        f.flush()?;
        Ok(())
    }

1.77.0 · Source

#### pub fn create_new<P: AsRef<Path>>(path: P) -> Result<File>

Creates a new file in read-write mode; error if the file exists.

This function will create a file if it does not exist, or return an error if it does. This way, if the call succeeds, the file returned is guaranteed to be new. If a file exists at the target location, creating a new file will fail with `AlreadyExists` or another error based on the situation. See `OpenOptions::open` for a non-exhaustive list of likely errors.

This option is useful because it is atomic. Otherwise between checking whether a file exists and creating a new one, the file may have been created by another process (a TOCTOU race condition / attack).

This can also be written using `File::options().read(true).write(true).create_new(true).open(...)`.

##### §Examples

    use std::fs::File;
    use std::io::Write;

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

1.58.0 · Source

#### pub fn options() -> OpenOptions

Returns a new OpenOptions object.

This function returns a new OpenOptions object that you can use to open or create a file with specific options if `open()` or `create()` are not appropriate.

It is equivalent to `OpenOptions::new()`, but allows you to write more readable code. Instead of `OpenOptions::new().append(true).open("example.log")`, you can write `File::options().append(true).open("example.log")`. This also avoids the need to import `OpenOptions`.

See the `OpenOptions::new` function for more details.

##### §Examples

    use std::fs::File;
    use std::io::Write;

    fn main() -> std::io::Result<()> {
        let mut f = File::options().append(true).open("example.log")?;
        writeln!(&mut f, "new line")?;
        Ok(())
    }

1.0.0 · Source

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

Attempts to sync all OS-internal file content and metadata to disk.

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

This can be used to handle errors that would otherwise only be caught when the `File` is closed, as dropping a `File` will ignore all errors. Note, however, that `sync_all` is generally more expensive than closing a file by dropping it, because the latter is not required to block until the data has been written to the filesystem.

If synchronizing the metadata is not required, use `sync_data` instead.

##### §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(())
    }

1.0.0 · Source

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

This function is similar to `sync_all`, except that it might 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(())
    }

1.89.0 · Source

#### pub fn lock(&self) -> Result<()>

Acquire an exclusive lock on the file. Blocks until the lock can be acquired.

This acquires an exclusive lock; no other file handle to this file may acquire another lock.

This lock may be advisory or mandatory. This lock is meant to interact with `lock`, `try_lock`, `lock_shared`, `try_lock_shared`, and `unlock`. Its interactions with other methods, such as `read` and `write` are platform specific, and it may or may not cause non-lockholders to block.

If this file handle/descriptor, or a clone of it, already holds a lock the exact behavior is unspecified and platform dependent, including the possibility that it will deadlock. However, if this method returns, then an exclusive lock is held.

If the file is not open for writing, it is unspecified whether this function returns an error.

The lock will be released when this file (along with any other file descriptors/handles duplicated or inherited from it) is closed, or if the `unlock` method is called.

##### §Platform-specific behavior

This function currently corresponds to the `flock` function on Unix with the `LOCK_EX` flag, and the `LockFileEx` function on Windows with the `LOCKFILE_EXCLUSIVE_LOCK` flag. Note that, this may change in the future.

On Windows, locking a file will fail if the file is opened only for append. To lock a file, open it with one of `.read(true)`, `.read(true).append(true)`, or `.write(true)`.

##### §Examples

    use std::fs::File;

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

1.89.0 · Source

#### pub fn lock_shared(&self) -> Result<()>

Acquire a shared (non-exclusive) lock on the file. Blocks until the lock can be acquired.

This acquires a shared lock; more than one file handle may hold a shared lock, but none may hold an exclusive lock at the same time.

This lock may be advisory or mandatory. This lock is meant to interact with `lock`, `try_lock`, `lock_shared`, `try_lock_shared`, and `unlock`. Its interactions with other methods, such as `read` and `write` are platform specific, and it may or may not cause non-lockholders to block.

If this file handle/descriptor, or a clone of it, already holds a lock, the exact behavior is unspecified and platform dependent, including the possibility that it will deadlock. However, if this method returns, then a shared lock is held.

The lock will be released when this file (along with any other file descriptors/handles duplicated or inherited from it) is closed, or if the `unlock` method is called.

##### §Platform-specific behavior

This function currently corresponds to the `flock` function on Unix with the `LOCK_SH` flag, and the `LockFileEx` function on Windows. Note that, this may change in the future.

On Windows, locking a file will fail if the file is opened only for append. To lock a file, open it with one of `.read(true)`, `.read(true).append(true)`, or `.write(true)`.

##### §Examples

    use std::fs::File;

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

1.89.0 · Source

#### pub fn try_lock(&self) -> Result<(), TryLockError>

Try to acquire an exclusive lock on the file.

Returns `Err(TryLockError::WouldBlock)` if a different lock is already held on this file (via another handle/descriptor).

This acquires an exclusive lock; no other file handle to this file may acquire another lock.

This lock may be advisory or mandatory. This lock is meant to interact with `lock`, `try_lock`, `lock_shared`, `try_lock_shared`, and `unlock`. Its interactions with other methods, such as `read` and `write` are platform specific, and it may or may not cause non-lockholders to block.

If this file handle/descriptor, or a clone of it, already holds a lock, the exact behavior is unspecified and platform dependent, including the possibility that it will deadlock. However, if this method returns `Ok(())`, then it has acquired an exclusive lock.

If the file is not open for writing, it is unspecified whether this function returns an error.

The lock will be released when this file (along with any other file descriptors/handles duplicated or inherited from it) is closed, or if the `unlock` method is called.

##### §Platform-specific behavior

This function currently corresponds to the `flock` function on Unix with the `LOCK_EX` and `LOCK_NB` flags, and the `LockFileEx` function on Windows with the `LOCKFILE_EXCLUSIVE_LOCK` and `LOCKFILE_FAIL_IMMEDIATELY` flags. Note that, this may change in the future.

On Windows, locking a file will fail if the file is opened only for append. To lock a file, open it with one of `.read(true)`, `.read(true).append(true)`, or `.write(true)`.

##### §Examples

    use std::fs::{File, TryLockError};

    fn main() -> std::io::Result<()> {
        let f = File::create("foo.txt")?;
        // Explicit handling of the WouldBlock error
        match f.try_lock() {
            Ok(_) => (),
            Err(TryLockError::WouldBlock) => (), // Lock not acquired
            Err(TryLockError::Error(err)) => return Err(err),
        }
        // Alternately, propagate the error as an io::Error
        f.try_lock()?;
        Ok(())
    }

1.89.0 · Source

#### pub fn try_lock_shared(&self) -> Result<(), TryLockError>

Try to acquire a shared (non-exclusive) lock on the file.

Returns `Err(TryLockError::WouldBlock)` if a different lock is already held on this file (via another handle/descriptor).

This acquires a shared lock; more than one file handle may hold a shared lock, but none may hold an exclusive lock at the same time.

This lock may be advisory or mandatory. This lock is meant to interact with `lock`, `try_lock`, `lock_shared`, `try_lock_shared`, and `unlock`. Its interactions with other methods, such as `read` and `write` are platform specific, and it may or may not cause non-lockholders to block.

If this file handle, or a clone of it, already holds a lock, the exact behavior is unspecified and platform dependent, including the possibility that it will deadlock. However, if this method returns `Ok(())`, then it has acquired a shared lock.

The lock will be released when this file (along with any other file descriptors/handles duplicated or inherited from it) is closed, or if the `unlock` method is called.

##### §Platform-specific behavior

This function currently corresponds to the `flock` function on Unix with the `LOCK_SH` and `LOCK_NB` flags, and the `LockFileEx` function on Windows with the `LOCKFILE_FAIL_IMMEDIATELY` flag. Note that, this may change in the future.

On Windows, locking a file will fail if the file is opened only for append. To lock a file, open it with one of `.read(true)`, `.read(true).append(true)`, or `.write(true)`.

##### §Examples

    use std::fs::{File, TryLockError};

    fn main() -> std::io::Result<()> {
        let f = File::open("foo.txt")?;
        // Explicit handling of the WouldBlock error
        match f.try_lock_shared() {
            Ok(_) => (),
            Err(TryLockError::WouldBlock) => (), // Lock not acquired
            Err(TryLockError::Error(err)) => return Err(err),
        }
        // Alternately, propagate the error as an io::Error
        f.try_lock_shared()?;

        Ok(())
    }

1.89.0 · Source

#### pub fn unlock(&self) -> Result<()>

Release all locks on the file.

All locks are released when the file (along with any other file descriptors/handles duplicated or inherited from it) is closed. This method allows releasing locks without closing the file.

If no lock is currently held via this file descriptor/handle, this method may return an error, or may return successfully without taking any action.

##### §Platform-specific behavior

This function currently corresponds to the `flock` function on Unix with the `LOCK_UN` flag, and the `UnlockFile` function on Windows. Note that, this may change in the future.

On Windows, locking a file will fail if the file is opened only for append. To lock a file, open it with one of `.read(true)`, `.read(true).append(true)`, or `.write(true)`.

##### §Examples

    use std::fs::File;

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

1.0.0 · Source

#### pub 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.

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. Also, `std::io::ErrorKind::InvalidInput` will be returned if the desired length would cause an overflow due to the implementation specifics.

##### §Examples

    use std::fs::File;

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

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

1.0.0 · Source

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

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(())
    }

1.9.0 · Source

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

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(())
    }

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(())
    }

1.16.0 · Source

#### pub fn set_permissions(&self, perm: Permissions) -> Result<()>

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(())
    }

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

1.75.0 · Source

#### pub fn set_times(&self, times: FileTimes) -> Result<()>

Changes the timestamps of the underlying file.

##### §Platform-specific behavior

This function currently corresponds to the `futimens` function on Unix (falling back to `futimes` on macOS before 10.13) and the `SetFileTime` function on Windows. Note that this may change in the future.

On most platforms, including UNIX and Windows platforms, this function can also change the timestamps of a directory. To get a `File` representing a directory in order to call `set_times`, open the directory with `File::open` without attempting to obtain write permission.

##### §Errors

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

This function may return an error if the operating system lacks support to change one or more of the timestamps set in the `FileTimes` structure.

##### §Examples

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

        let src = fs::metadata("src")?;
        let dest = File::open("dest")?;
        let times = FileTimes::new()
            .set_accessed(src.accessed()?)
            .set_modified(src.modified()?);
        dest.set_times(times)?;
        Ok(())
    }

1.75.0 · Source

#### pub fn set_modified(&self, time: SystemTime) -> Result<()>

Changes the modification time of the underlying file.

This is an alias for `set_times(FileTimes::new().set_modified(time))`.

## Trait Implementations§

1.63.0 · Source§

### impl AsFd for File

Available on (Unix or HermitCore or `target_os=trusty` or WASI or `target_os=motor`) and non-`target_os=trusty` only.
Source§

#### fn as_fd(&self) -> BorrowedFd<'_>

Borrows the file descriptor. Read more
1.0.0 · Source§

### impl AsRawFd for File

Available on (Unix or HermitCore or `target_os=trusty` or WASI or `target_os=motor`) and non-`target_os=trusty` only.
Source§

#### fn as_raw_fd(&self) -> RawFd

Extracts the raw file descriptor. Read more
1.0.0 · Source§

### impl Debug for File

Source§

#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
1.63.0 · Source§

### impl From<File> for OwnedFd

Available on (Unix or HermitCore or `target_os=trusty` or WASI or `target_os=motor`) and non-`target_os=trusty` only.
Source§

#### fn from(file: File) -> OwnedFd

Takes ownership of a `File`’s underlying file descriptor.

1.20.0 · Source§

### impl From<File> for Stdio

Source§

#### fn from(file: File) -> Stdio

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")?;

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

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

1.63.0 · Source§

### impl From<OwnedFd> for File

Available on (Unix or HermitCore or `target_os=trusty` or WASI or `target_os=motor`) and non-`target_os=trusty` only.
Source§

#### fn from(owned_fd: OwnedFd) -> Self

Returns a `File` that takes ownership of the given file descriptor.

1.1.0 · Source§

### impl FromRawFd for File

Available on (Unix or HermitCore or `target_os=trusty` or WASI or `target_os=motor`) and non-`target_os=trusty` only.
Source§

#### unsafe fn from_raw_fd(fd: RawFd) -> File ⓘ

Constructs a new instance of `Self` from the given raw file descriptor. Read more
1.4.0 · Source§

### impl IntoRawFd for File

Available on (Unix or HermitCore or `target_os=trusty` or WASI or `target_os=motor`) and non-`target_os=trusty` only.
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#### fn into_raw_fd(self) -> RawFd

Consumes this object, returning the raw underlying file descriptor. Read more
1.70.0 · Source§

### impl IsTerminal for File

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#### fn is_terminal(&self) -> bool

Returns `true` if the descriptor/handle refers to a terminal/tty. Read more
1.0.0 · Source§

### impl Read for &File

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

Reads some bytes from the file.

See `Read::read` docs for more info.

##### §Platform-specific behavior

This function currently corresponds to the `read` function on Unix and the `NtReadFile` function on Windows. Note that this may change in the future.

Source§

#### fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>

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

See `Read::read_vectored` docs for more info.

##### §Platform-specific behavior

This function currently corresponds to the `readv` function on Unix and falls back to the `read` implementation on Windows. Note that this may change in the future.

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#### fn is_read_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (`can_vector` #69941)

Determines if `File` has an efficient `read_vectored` implementation.

See `Read::is_read_vectored` docs for more info.

##### §Platform-specific behavior

This function currently returns `true` on Unix and `false` on Windows. Note that this may change in the future.

Source§

#### fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>

🔬This is a nightly-only experimental API. (`read_buf` #78485)
Pull some bytes from this source into the specified buffer. Read more
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#### fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>

Reads all bytes until EOF in this source, placing them into `buf`. Read more
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#### fn read_to_string(&mut self, buf: &mut String) -> Result<usize>

Reads all bytes until EOF in this source, appending them to `buf`. Read more
1.6.0 · Source§

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

Reads the exact number of bytes required to fill `buf`. Read more
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#### fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>

🔬This is a nightly-only experimental API. (`read_buf` #78485)
Reads the exact number of bytes required to fill `cursor`. Read more
1.0.0 · Source§

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

Creates a “by reference” adapter for this instance of `Read`. Read more
1.0.0 · Source§

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

Transforms this `Read` instance to an `Iterator` over its bytes. Read more
1.0.0 · Source§

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

Creates an adapter which will chain this stream with another. Read more
1.0.0 · Source§

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

Creates an adapter which will read at most `limit` bytes from it. Read more
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#### fn read_array<const N: usize>(&mut self) -> Result<[u8; N]>
where Self: Sized,

🔬This is a nightly-only experimental API. (`read_array` #148848)
Read and return a fixed array of bytes from this source. Read more
1.0.0 · Source§

### impl Read for File

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#### 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. Read more
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#### fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>

Like `read`, except that it reads into a slice of buffers. Read more
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#### fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>

🔬This is a nightly-only experimental API. (`read_buf` #78485)
Pull some bytes from this source into the specified buffer. Read more
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#### fn is_read_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (`can_vector` #69941)
Determines if this `Read`er has an efficient `read_vectored` implementation. Read more
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#### fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>

Reads all bytes until EOF in this source, placing them into `buf`. Read more
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#### fn read_to_string(&mut self, buf: &mut String) -> Result<usize>

Reads all bytes until EOF in this source, appending them to `buf`. Read more
1.6.0 · Source§

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

Reads the exact number of bytes required to fill `buf`. Read more
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#### fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>

🔬This is a nightly-only experimental API. (`read_buf` #78485)
Reads the exact number of bytes required to fill `cursor`. Read more
1.0.0 · Source§

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

Creates a “by reference” adapter for this instance of `Read`. Read more
1.0.0 · Source§

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

Transforms this `Read` instance to an `Iterator` over its bytes. Read more
1.0.0 · Source§

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

Creates an adapter which will chain this stream with another. Read more
1.0.0 · Source§

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

Creates an adapter which will read at most `limit` bytes from it. Read more
Source§

#### fn read_array<const N: usize>(&mut self) -> Result<[u8; N]>
where Self: Sized,

🔬This is a nightly-only experimental API. (`read_array` #148848)
Read and return a fixed array of bytes from this source. Read more
1.0.0 · Source§

### impl Seek for &File

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

Seek to an offset, in bytes in a file.

See `Seek::seek` docs for more info.

##### §Platform-specific behavior

This function currently corresponds to the `lseek64` function on Unix and the `SetFilePointerEx` function on Windows. Note that this may change in the future.

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#### fn stream_len(&mut self) -> Result<u64>

🔬This is a nightly-only experimental API. (`seek_stream_len` #59359)

Returns the length of this file (in bytes).

See `Seek::stream_len` docs for more info.

##### §Platform-specific behavior

This function currently corresponds to the `statx` function on Linux (with fallbacks) and the `GetFileSizeEx` function on Windows. Note that this may change in the future.

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#### fn stream_position(&mut self) -> Result<u64>

Returns the current seek position from the start of the stream. Read more
1.55.0 · Source§

#### fn rewind(&mut self) -> Result<()>

Rewind to the beginning of a stream. Read more
1.80.0 · Source§

#### fn seek_relative(&mut self, offset: i64) -> Result<()>

Seeks relative to the current position. Read more
1.0.0 · Source§

### impl Seek for File

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

Seek to an offset, in bytes, in a stream. Read more
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#### fn stream_len(&mut self) -> Result<u64>

🔬This is a nightly-only experimental API. (`seek_stream_len` #59359)
Returns the length of this stream (in bytes). Read more
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#### fn stream_position(&mut self) -> Result<u64>

Returns the current seek position from the start of the stream. Read more
1.55.0 · Source§

#### fn rewind(&mut self) -> Result<()>

Rewind to the beginning of a stream. Read more
1.80.0 · Source§

#### fn seek_relative(&mut self, offset: i64) -> Result<()>

Seeks relative to the current position. Read more
1.0.0 · Source§

### impl Write for &File

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

Writes some bytes to the file.

See `Write::write` docs for more info.

##### §Platform-specific behavior

This function currently corresponds to the `write` function on Unix and the `NtWriteFile` function on Windows. Note that this may change in the future.

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#### fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>

Like `write`, except that it writes into a slice of buffers.

See `Write::write_vectored` docs for more info.

##### §Platform-specific behavior

This function currently corresponds to the `writev` function on Unix and falls back to the `write` implementation on Windows. Note that this may change in the future.

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#### fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (`can_vector` #69941)

Determines if `File` has an efficient `write_vectored` implementation.

See `Write::is_write_vectored` docs for more info.

##### §Platform-specific behavior

This function currently returns `true` on Unix and `false` on Windows. Note that this may change in the future.

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

Flushes the file, ensuring that all intermediately buffered contents reach their destination.

See `Write::flush` docs for more info.

##### §Platform-specific behavior

Since a `File` structure doesn’t contain any buffers, this function is currently a no-op on Unix and Windows. Note that this may change in the future.

1.0.0 · Source§

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

Attempts to write an entire buffer into this writer. Read more
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#### fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>

🔬This is a nightly-only experimental API. (`write_all_vectored` #70436)
Attempts to write multiple buffers into this writer. Read more
1.0.0 · Source§

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

Writes a formatted string into this writer, returning any error encountered. Read more
1.0.0 · Source§

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

Creates a “by reference” adapter for this instance of `Write`. Read more
1.0.0 · Source§

### impl Write for File

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

Writes a buffer into this writer, returning how many bytes were written. Read more
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#### fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>

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

#### fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (`can_vector` #69941)
Determines if this `Write`r has an efficient `write_vectored` implementation. Read more
Source§

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

Flushes this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
1.0.0 · Source§

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

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

#### fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>

🔬This is a nightly-only experimental API. (`write_all_vectored` #70436)
Attempts to write multiple buffers into this writer. Read more
1.0.0 · Source§

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

Writes a formatted string into this writer, returning any error encountered. Read more
1.0.0 · Source§

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

Creates a “by reference” adapter for this instance of `Write`. Read more

## Auto Trait Implementations§

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### impl Freeze for File

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### impl RefUnwindSafe for File

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### impl Send for File

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### impl Sync for File

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### impl Unpin for File

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### impl UnwindSafe for File

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.