# Struct ethcore_util::standard::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

    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>(path: P) -> Result<File, Error> where P: AsRef<Path>`

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

#### `fn create<P>(path: P) -> Result<File, Error> where P: AsRef<Path>`

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

#### `fn sync_all(&self) -> Result<(), Error>`

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

    try!(f.sync_all());

#### `fn sync_data(&self) -> Result<(), Error>`

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

    try!(f.sync_data());

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

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

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

Queries metadata about the underlying file.

# Examples

    use std::fs::File;

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

#### `fn try_clone(&self) -> Result<File, Error>`
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 = try!(File::open("foo.txt"));
    let file_copy = try!(f.try_clone());

## Trait Implementations

### `impl FromRawFd for File`
1.1.0

#### `unsafe fn from_raw_fd(fd: i32) -> File`

### `impl FileExt for File`

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

Unstable (`file_offset`)

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

Unstable (`file_offset`)

### `impl AsRawFd for File`

#### `fn as_raw_fd(&self) -> i32`

### `impl Write for File`

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

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

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

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

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

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

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

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

#### `fn by_ref(&mut self) -> &mut Self`

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

### `impl<'a> Write for &'a File`

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

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

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

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

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

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

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

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

#### `fn by_ref(&mut self) -> &mut Self`

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

### `impl Debug for File`

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

Formats the value using the given formatter.

### `impl IntoRawFd for File`
1.4.0

#### `fn into_raw_fd(self) -> i32`

### `impl Read for File`

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

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

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

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, Error>`

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

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

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

#### `fn by_ref(&mut self) -> &mut Self`

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

#### `fn bytes(self) -> Bytes<Self>`

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

#### `fn chars(self) -> Chars<Self>`

Unstable (`io`)

: 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>(self, next: R) -> Chain<Self, R> where R: Read`

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

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

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

### `impl<'a> Read for &'a File`

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

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

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

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, Error>`

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

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

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

#### `fn by_ref(&mut self) -> &mut Self`

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

#### `fn bytes(self) -> Bytes<Self>`

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

#### `fn chars(self) -> Chars<Self>`

Unstable (`io`)

: 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>(self, next: R) -> Chain<Self, R> where R: Read`

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

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

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

### `impl Seek for File`

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

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

### `impl<'a> Seek for &'a File`

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

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

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