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. 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 Read
er. 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: 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; fn main() -> std::io::Result<()> { let mut f = File::open("foo.txt")?; Ok(()) }
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.
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
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<()>
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<()>
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(()) }
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
.
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(()) }
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(()) }
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
.
Trait Implementations
impl AsFd for File
fn as_fd(&self) -> BorrowedFd<'_>
Borrows the file descriptor. Read more
impl AsRawFd for File
fn as_raw_fd(&self) -> RawFd
Extracts the raw file descriptor. Read more
fn as_raw_handle(&self) -> RawHandle
Extracts the raw handle, without taking any ownership.
impl Debug for File
fn fmt(&self, f: &mut Formatter<'_>) -> Result
Formats the value using the given formatter. Read more
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
fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
Reads the exact number of byte required to fill buf
from the given offset. Read more
fn write_all_at(&self, buf: &[u8], offset: u64) -> Result<()>
Attempts to write an entire buffer starting from a given offset. Read more
fn read_vectored_at(
&self,
bufs: &mut [IoSliceMut<'_>],
offset: u64
) -> Result<usize>
Reads a number of bytes starting from a given offset. Read more
fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> Result<usize>
Writes a number of bytes starting from a given offset. Read more
fn tell(&self) -> Result<u64>
Returns the current position within the file. Read more
fn fdstat_set_flags(&self, flags: u16) -> Result<()>
Adjust the flags associated with this file. Read more
fn fdstat_set_rights(&self, rights: u64, inheriting: u64) -> Result<()>
Adjust the rights associated with this file. Read more
fn advise(&self, offset: u64, len: u64, advice: u8) -> Result<()>
Provide file advisory information on a file descriptor. Read more
fn allocate(&self, offset: u64, len: u64) -> Result<()>
Force the allocation of space in a file. Read more
fn create_directory<P: AsRef<Path>>(&self, dir: P) -> Result<()>
Create a directory. Read more
fn read_link<P: AsRef<Path>>(&self, path: P) -> Result<PathBuf>
Read the contents of a symbolic link. Read more
fn metadata_at<P: AsRef<Path>>(
&self,
lookup_flags: u32,
path: P
) -> Result<Metadata>
Return the attributes of a file or directory. Read more
fn remove_file<P: AsRef<Path>>(&self, path: P) -> Result<()>
Unlink a file. Read more
fn remove_directory<P: AsRef<Path>>(&self, path: P) -> Result<()>
Remove a directory. Read more
fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
Reads a number of bytes starting from a given offset. Read more
fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
Reads the exact number of byte required to fill buf
from the 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
fn write_all_at(&self, buf: &[u8], offset: u64) -> Result<()>
Attempts to write an entire buffer starting from a given offset. Read more
fn seek_read(&self, buf: &mut [u8], offset: u64) -> Result<usize>
Seeks to a given position and reads a number of bytes. Read more
fn seek_write(&self, buf: &[u8], offset: u64) -> Result<usize>
Seeks to a given position and writes a number of bytes. Read more
fn from(file: File) -> OwnedHandle
Performs the conversion.
impl From<File> for OwnedFd
fn from(file: File) -> OwnedFd
Performs the conversion.
impl From<File> for Stdio
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").unwrap(); let reverse = Command::new("rev") .stdin(file) // Implicit File conversion into a Stdio .output() .expect("failed reverse command"); assert_eq!(reverse.stdout, b"!dlrow ,olleH");
impl From<OwnedFd> for File
fn from(owned_fd: OwnedFd) -> Self
Performs the conversion.
fn from(owned: OwnedHandle) -> Self
Performs the conversion.
impl FromRawFd for File
unsafe fn from_raw_fd(fd: RawFd) -> File
impl Read for File impl Read for &File impl Write for File impl Write for &File
Constructs a new instance of Self
from the given raw file descriptor. Read more
unsafe fn from_raw_handle(handle: RawHandle) -> File
impl Read for File impl Read for &File impl Write for File impl Write for &File
Constructs a new I/O object from the specified raw handle. Read more
impl IntoRawFd for File
fn into_raw_fd(self) -> RawFd
Consumes this object, returning the raw underlying file descriptor. Read more
fn into_raw_handle(self) -> RawHandle
Consumes this object, returning the raw underlying handle. Read more
impl Read for File
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
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
Like read
, except that it reads into a slice of buffers. Read more
fn is_read_vectored(&self) -> bool
Determines if this Read
er has an efficient read_vectored
implementation. Read more
unsafe fn initializer(&self) -> Initializer
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, appending them to buf
. Read more
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
Read the exact number of bytes required to fill buf
. Read more
Creates a “by reference” adapter for this instance of Read
. Read more
impl<R: Read> Iterator for Bytes<R> type Item = Result<u8>;
impl<T: Read, U: Read> Read for Chain<T, U>
Creates an adapter which will chain this stream with another. Read more
impl<T: Read> Read for Take<T>
Creates an adapter which will read at most limit
bytes from it. Read more
impl Read for &File
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
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
Like read
, except that it reads into a slice of buffers. Read more
fn is_read_vectored(&self) -> bool
Determines if this Read
er has an efficient read_vectored
implementation. Read more
unsafe fn initializer(&self) -> Initializer
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, appending them to buf
. Read more
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
Read the exact number of bytes required to fill buf
. Read more
Creates a “by reference” adapter for this instance of Read
. Read more
impl<R: Read> Iterator for Bytes<R> type Item = Result<u8>;
impl<T: Read, U: Read> Read for Chain<T, U>
Creates an adapter which will chain this stream with another. Read more
impl<T: Read> Read for Take<T>
Creates an adapter which will read at most limit
bytes from it. Read more
impl Seek for File
fn seek(&mut self, pos: SeekFrom) -> Result<u64>
Seek to an offset, in bytes, in a stream. Read more
fn rewind(&mut self) -> Result<()>
Rewind to the beginning of a stream. Read more
fn stream_len(&mut self) -> Result<u64>
Returns the length of this stream (in bytes). Read more
fn stream_position(&mut self) -> Result<u64>
Returns the current seek position from the start of the stream. Read more
impl Seek for &File
fn seek(&mut self, pos: SeekFrom) -> Result<u64>
Seek to an offset, in bytes, in a stream. Read more
fn rewind(&mut self) -> Result<()>
Rewind to the beginning of a stream. Read more
fn stream_len(&mut self) -> Result<u64>
Returns the length of this stream (in bytes). Read more
fn stream_position(&mut self) -> Result<u64>
Returns the current seek position from the start of the stream. Read more
impl Write for File
fn write(&mut self, buf: &[u8]) -> Result<usize>
Write a buffer into this writer, returning how many bytes were written. Read more
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn is_write_vectored(&self) -> bool
Determines if this Write
r has an efficient write_vectored
implementation. 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 writer. Read more
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
Attempts to write multiple buffers into this writer. Read more
fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>
Writes a formatted string into this writer, returning any error encountered. Read more
Creates a “by reference” adapter for this instance of Write
. Read more
impl Write for &File
fn write(&mut self, buf: &[u8]) -> Result<usize>
Write a buffer into this writer, returning how many bytes were written. Read more
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn is_write_vectored(&self) -> bool
Determines if this Write
r has an efficient write_vectored
implementation. 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 writer. Read more
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
Attempts to write multiple buffers into this writer. Read more
fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>
Writes a formatted string into this writer, returning any error encountered. Read more
Creates a “by reference” adapter for this instance of Write
. Read more
Auto Trait Implementations
impl RefUnwindSafe for File
impl Send for File
impl Sync for File
impl Unpin for File
impl UnwindSafe for File
Blanket Implementations
impl<T> From<T> for T
pub fn from(t: T) -> T
Performs the conversion.
pub fn into(self) -> U
Performs the conversion.
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
Performs the conversion.
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
Performs the conversion.
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/fs/struct.File.html