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

Create 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]

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

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

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

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

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.

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

Create 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

Create 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

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]

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

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

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

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

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

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

Important traits for &'_ mut I

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

Important traits for Bytes<R>

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

Important traits for Chain<T, U>

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

Important traits for Take<T>

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

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

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

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

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

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

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

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

Important traits for &'_ mut I

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

Important traits for Bytes<R>

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

Important traits for Chain<T, U>

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

Important traits for Take<T>

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

impl Write for File
[src]

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

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

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

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

Important traits for &'_ mut I

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

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

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

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

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

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

Important traits for &'_ mut I

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

impl Seek for File
[src]

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

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

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

impl AsRawFd for File
[src]

This is supported on Unix only.

Extracts the raw file descriptor. Read more

impl FromRawFd for File
1.1.0
[src]

Important traits for File

This is supported on Unix only.

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

impl IntoRawFd for File
1.4.0
[src]

This is supported on Unix only.

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

impl FileExt for File
1.15.0
[src]

This is supported on Unix only.

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

This is supported on Unix only.

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

🔬 This is a nightly-only experimental API. (rw_exact_all_at #51984)
This is supported on Unix only.

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

🔬 This is a nightly-only experimental API. (rw_exact_all_at #51984)
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]

This is supported on Windows only.

Seeks to a given position and reads a number of bytes. Read more

This is supported on Windows only.

Seeks to a given position and writes a number of bytes. Read more

impl AsRawHandle for File
[src]

This is supported on Windows only.

Extracts the raw handle, without taking any ownership.

impl FromRawHandle for File
1.1.0
[src]

Important traits for File

This is supported on Windows only.

Constructs a new I/O object from the specified raw handle. Read more

impl IntoRawHandle for File
1.4.0
[src]

This is supported on Windows only.

Consumes this object, returning the raw underlying handle. Read more

impl Debug for File
[src]

Formats the value using the given formatter. Read more

impl From<File> for Stdio
1.20.0
[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 convertion 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, U> TryFrom for T where
    T: From<U>, 
[src]

🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

🔬 This is a nightly-only experimental API. (try_from #33417)

Performs the conversion.

impl<T> From for T
[src]

Performs the conversion.

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

🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

🔬 This is a nightly-only experimental API. (try_from #33417)

Performs the conversion.

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

Performs the conversion.

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

Important traits for &'_ mut I

Immutably borrows from an owned value. Read more

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

Important traits for &'_ mut I

Mutably borrows from an owned value. Read more

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

🔬 This is a nightly-only experimental API. (get_type_id #27745)

this method will likely be replaced by an associated static

Gets the TypeId of self. Read more