Struct rhit::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. Errors detected on closing are ignored by the implementation of Drop. Use the method sync_all if these errors must be manually handled.

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(())
}

Read 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(())
}

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(())
}

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.

Implementations

impl File

pub 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;

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

pub 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;

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

pub fn with_options() -> OpenOptions

🔬 This is a nightly-only experimental API. (with_options)

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().read(true).open("foo.txt") you can write File::with_options().read(true).open("foo.txt"). This also avoids the need to import OpenOptions.

See the OpenOptions::new function for more details.

Examples

#![feature(with_options)]
use std::fs::File;

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

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

Attempts to sync all OS-internal 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. Dropping a file will ignore errors in synchronizing this in-memory data.

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(())
}

pub 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::*;

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

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

pub 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.

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.

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

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(())
}

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

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(())
}

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

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.

Trait Implementations

impl AsRawFd for File

pub fn as_raw_fd(&self) -> i32

Extracts the raw file descriptor.

impl Debug for File

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

Formats the value using the given formatter.

impl FileExt for File

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

Reads a number of bytes starting from a given offset.

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

Writes a number of bytes starting from a given offset.

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

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

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

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

impl FromRawFd for File

pub unsafe fn from_raw_fd(fd: i32) -> File

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

impl IntoRawFd for File

pub fn into_raw_fd(self) -> i32

Consumes this object, returning the raw underlying file descriptor.

impl<'_> Read for &'_ File

pub 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.

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

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

pub fn is_read_vectored(&self) -> bool

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

Determines if this Reader has an efficient read_vectored implementation.

pub unsafe fn initializer(&self) -> Initializer

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

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

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

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

pub fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

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

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

Read the exact number of bytes required to fill buf.

pub fn by_ref(&mut self) -> &mut Self

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

pub fn bytes(self) -> Bytes<Self>

Transforms this Read instance to an Iterator over its bytes.

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

Creates an adaptor which will chain this stream with another.

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

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

impl Read for File

pub 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.

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

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

pub fn is_read_vectored(&self) -> bool

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

Determines if this Reader has an efficient read_vectored implementation.

pub unsafe fn initializer(&self) -> Initializer

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

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

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

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

pub fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

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

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

Read the exact number of bytes required to fill buf.

pub fn by_ref(&mut self) -> &mut Self

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

pub fn bytes(self) -> Bytes<Self>

Transforms this Read instance to an Iterator over its bytes.

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

Creates an adaptor which will chain this stream with another.

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

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

impl Seek for File

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

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

pub fn stream_len(&mut self) -> Result<u64, Error>

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

Returns the length of this stream (in bytes).

pub fn stream_position(&mut self) -> Result<u64, Error>

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

impl<'_> Seek for &'_ File

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

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

pub fn stream_len(&mut self) -> Result<u64, Error>

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

Returns the length of this stream (in bytes).

pub fn stream_position(&mut self) -> Result<u64, Error>

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

impl Write for File

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

Write a buffer into this writer, returning how many bytes were written.

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

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

pub fn is_write_vectored(&self) -> bool

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

Determines if this Writer has an efficient write_vectored implementation.

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

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

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

Attempts to write an entire buffer into this writer.

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

🔬 This is a nightly-only experimental API. (write_all_vectored)

Attempts to write multiple buffers into this writer.

pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<(), Error>

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

pub fn by_ref(&mut self) -> &mut Self

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

impl<'_> Write for &'_ File

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

Write a buffer into this writer, returning how many bytes were written.

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

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

pub fn is_write_vectored(&self) -> bool

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

Determines if this Writer has an efficient write_vectored implementation.

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

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

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

Attempts to write an entire buffer into this writer.

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

🔬 This is a nightly-only experimental API. (write_all_vectored)

Attempts to write multiple buffers into this writer.

pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<(), Error>

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

pub fn by_ref(&mut self) -> &mut Self

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