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

    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

Create a new file and write bytes to it:

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

    let mut file = File::create("foo.txt")?;
    file.write_all(b"Hello, world!")?;Run

Read the contents of a file into a `String`:

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

    let mut file = File::open("foo.txt")?;
    let mut contents = String::new();
    file.read_to_string(&mut contents)?;
    assert_eq!(contents, "Hello, world!");Run

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

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

    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!");Run

## Methods

### `impl File`
[src]

#### `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

    use std::fs::File;

    let mut f = File::open("foo.txt")?;Run

#### `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

    use std::fs::File;

    let mut f = File::create("foo.txt")?;Run

#### `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

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

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

    f.sync_all()?;Run

#### `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

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

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

    f.sync_data()?;Run

#### `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

    use std::fs::File;

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

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

Queries metadata about the underlying file.

# Examples

    use std::fs::File;

    let mut f = File::open("foo.txt")?;
    let metadata = f.metadata()?;Run

#### `fn try_clone(&self) -> Result<File>`
1.9.0

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.

# Examples

    use std::fs::File;

    let mut f = File::open("foo.txt")?;
    let file_copy = f.try_clone()?;Run

#### `fn set_permissions(&self, perm: Permissions) -> Result<()>`
1.16.0

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

    use std::fs::File;

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

## Trait Implementations

### `impl Debug for File`
[src]

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

Formats the value using the given formatter.

### `impl Read for File`
[src]

#### `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

#### `unsafe fn initializer(&self) -> Initializer`

🔬 This is a nightly-only experimental API. (`read_initializer` #42788)

Determines if this `Read`er can work with buffers of uninitialized memory. Read more

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

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>`

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

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

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

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

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

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

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

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

🔬 This is a nightly-only experimental API. (`io` #27802)

the semantics of a partial read/write of where errors happen is currently unclear and may change

Transforms this `Read` instance to an `Iterator` over `char`s. Read more

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

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

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

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

### `impl Write for File`
[src]

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

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

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

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

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

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

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

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

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

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

### `impl Seek for File`
[src]

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

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

### `impl<'a> Read for &'a File`
[src]

#### `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

#### `unsafe fn initializer(&self) -> Initializer`

🔬 This is a nightly-only experimental API. (`read_initializer` #42788)

Determines if this `Read`er can work with buffers of uninitialized memory. Read more

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

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>`

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

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

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

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

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

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

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

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

🔬 This is a nightly-only experimental API. (`io` #27802)

the semantics of a partial read/write of where errors happen is currently unclear and may change

Transforms this `Read` instance to an `Iterator` over `char`s. Read more

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

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

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

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

### `impl<'a> Write for &'a File`
[src]

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

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

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

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

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

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

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

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

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

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

### `impl<'a> Seek for &'a File`
[src]

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

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

### `impl AsRawFd for File`
[src]

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

Extracts the raw file descriptor. Read more

### `impl FromRawFd for File`
1.1.0
[src]

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

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

### `impl IntoRawFd for File`
1.4.0
[src]

#### `fn into_raw_fd(self) -> RawFd`

Consumes this object, returning the raw underlying file descriptor. Read more

### `impl FileExt for File`
1.15.0
[src]

#### `fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>`

Reads a number of bytes starting from a given offset. Read more

#### `fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize>`

Writes a number of bytes starting from a given offset. Read more

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