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Struct std::fs::File
pub struct File { /* private fields */ }
An object providing access 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.
Platform-specific behavior
On Windows, the implementation of Read
and Write
traits for File
perform synchronous I/O operations. Therefore the underlying file must not have been opened for asynchronous I/O (e.g. by using FILE_FLAG_OVERLAPPED
).
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.
If you only need to read the entire file contents, consider std::fs::read()
or std::fs::read_to_string()
instead.
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;
use std::io::Read;
fn main() -> std::io::Result<()> {
let mut f = File::open("foo.txt")?;
let mut data = vec![];
f.read_to_end(&mut data)?;
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.
Depending on the platform, this function may fail if the full directory path does not exist. See the OpenOptions::open
function for more details.
See also std::fs::write()
for a simple function to create a file with a given data.
Examples
use std::fs::File;
use std::io::Write;
fn main() -> std::io::Result<()> {
let mut f = File::create("foo.txt")?;
f.write_all(&1234_u32.to_be_bytes())?;
Ok(())
}
pub fn create_new<P: AsRef<Path>>(path: P) -> Result<File>
file_create_new
#105135)
Creates a new file in read-write mode; error if the file exists.
This function will create a file if it does not exist, or return an error if it does. This way, if the call succeeds, the file returned is guaranteed to be new.
This option is useful because it is atomic. Otherwise between checking whether a file exists and creating a new one, the file may have been created by another process (a TOCTOU race condition / attack).
This can also be written using File::options().read(true).write(true).create_new(true).open(...)
.
Examples
#![feature(file_create_new)]
use std::fs::File;
use std::io::Write;
fn main() -> std::io::Result<()> {
let mut f = File::create_new("foo.txt")?;
f.write_all("Hello, world!".as_bytes())?;
Ok(())
}
pub fn 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().append(true).open("example.log")
, you can write File::options().append(true).open("example.log")
. This also avoids the need to import OpenOptions
.
See the OpenOptions::new
function for more details.
Examples
use std::fs::File;
use std::io::Write;
fn main() -> std::io::Result<()> {
let mut f = File::options().append(true).open("example.log")?;
writeln!(&mut f, "new line")?;
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
.
pub fn set_times(&self, times: FileTimes) -> Result<()>
Changes the timestamps of the underlying file.
Platform-specific behavior
This function currently corresponds to the futimens
function on Unix (falling back to futimes
on macOS before 10.13) and the SetFileTime
function on Windows. Note that this may change in the future.
Errors
This function will return an error if the user lacks permission to change timestamps on the underlying file. It may also return an error in other os-specific unspecified cases.
This function may return an error if the operating system lacks support to change one or more of the timestamps set in the FileTimes
structure.
Examples
fn main() -> std::io::Result<()> {
use std::fs::{self, File, FileTimes};
let src = fs::metadata("src")?;
let dest = File::options().write(true).open("dest")?;
let times = FileTimes::new()
.set_accessed(src.accessed()?)
.set_modified(src.modified()?);
dest.set_times(times)?;
Ok(())
}
pub fn set_modified(&self, time: SystemTime) -> Result<()>
Changes the modification time of the underlying file.
This is an alias for set_times(FileTimes::new().set_modified(time))
.
Trait Implementations
impl AsFd for File
impl AsHandle for FileAvailable on Windows only.
impl AsRawFd for File
impl AsRawHandle for FileAvailable on Windows only.
impl Debug for File
fn fmt(&self, f: &mut Formatter<'_>) -> Result
impl FileExt for FileAvailable on Windows only.
fn seek_read(&self, buf: &mut [u8], offset: u64) -> Result<usize>
fn seek_write(&self, buf: &[u8], offset: u64) -> Result<usize>
impl FileExt for FileAvailable on WASI only.
fn read_vectored_at(
&self,
bufs: &mut [IoSliceMut<'_>],
offset: u64
) -> Result<usize>
wasi_ext
#71213)
fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> Result<usize>
wasi_ext
#71213)
fn tell(&self) -> Result<u64>
wasi_ext
#71213)
fn fdstat_set_flags(&self, flags: u16) -> Result<()>
wasi_ext
#71213)
fn fdstat_set_rights(&self, rights: u64, inheriting: u64) -> Result<()>
wasi_ext
#71213)
fn advise(&self, offset: u64, len: u64, advice: u8) -> Result<()>
wasi_ext
#71213)
fn allocate(&self, offset: u64, len: u64) -> Result<()>
wasi_ext
#71213)
fn create_directory<P: AsRef<Path>>(&self, dir: P) -> Result<()>
wasi_ext
#71213)
fn read_link<P: AsRef<Path>>(&self, path: P) -> Result<PathBuf>
wasi_ext
#71213)
fn metadata_at<P: AsRef<Path>>(
&self,
lookup_flags: u32,
path: P
) -> Result<Metadata>
wasi_ext
#71213)
fn remove_file<P: AsRef<Path>>(&self, path: P) -> Result<()>
wasi_ext
#71213)
fn remove_directory<P: AsRef<Path>>(&self, path: P) -> Result<()>
wasi_ext
#71213)
fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
wasi_ext
#71213)
fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
buf
from the given offset. Read more
fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize>
wasi_ext
#71213)
fn write_all_at(&self, buf: &[u8], offset: u64) -> Result<()>
impl FileExt for FileAvailable on Unix only.
fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
fn read_vectored_at(
&self,
bufs: &mut [IoSliceMut<'_>],
offset: u64
) -> Result<usize>
unix_file_vectored_at
#89517)
read_at
, except that it reads into a slice of buffers. Read more
fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize>
fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> Result<usize>
unix_file_vectored_at
#89517)
write_at
, except that it writes from a slice of buffers. Read more
fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
buf
from the given offset. Read more
fn write_all_at(&self, buf: &[u8], offset: u64) -> Result<()>
impl From<File> for OwnedFd
fn from(file: File) -> OwnedFd
impl From<File> for OwnedHandleAvailable on Windows only.
fn from(file: File) -> OwnedHandle
impl From<File> for Stdio
fn from(file: File) -> 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
impl From<OwnedHandle> for FileAvailable on Windows only.
fn from(owned: OwnedHandle) -> Self
impl FromRawFd for File
unsafe fn from_raw_fd(fd: RawFd) -> File ⓘ
Self
from the given raw file descriptor. Read more
impl FromRawHandle for FileAvailable on Windows only.
unsafe fn from_raw_handle(handle: RawHandle) -> File ⓘ
impl IntoRawFd for File
fn into_raw_fd(self) -> RawFd
impl IntoRawHandle for FileAvailable on Windows only.
fn into_raw_handle(self) -> RawHandle
impl IsTerminal for File
fn is_terminal(&self) -> bool
true
if the descriptor/handle refers to a terminal/tty. Read more
impl Read for &File
fn read(&mut self, buf: &mut [u8]) -> Result<usize>
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
read
, except that it reads into a slice of buffers. Read more
fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)
fn is_read_vectored(&self) -> bool
can_vector
#69941)
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
buf
. Read more
fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
buf
. Read more
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
buf
. Read more
fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)
cursor
. Read more
fn by_ref(&mut self) -> &mut Self
where
Self: Sized,
Read
. Read more
fn bytes(self) -> Bytes<Self> ⓘ
where
Self: Sized,
fn chain<R: Read>(self, next: R) -> Chain<Self, R> ⓘ
where
Self: Sized,
fn take(self, limit: u64) -> Take<Self> ⓘ
where
Self: Sized,
limit
bytes from it. Read more
impl Read for File
fn read(&mut self, buf: &mut [u8]) -> Result<usize>
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
read
, except that it reads into a slice of buffers. Read more
fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)
fn is_read_vectored(&self) -> bool
can_vector
#69941)
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
buf
. Read more
fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
buf
. Read more
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
buf
. Read more
fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)
cursor
. Read more
fn by_ref(&mut self) -> &mut Self
where
Self: Sized,
Read
. Read more
fn bytes(self) -> Bytes<Self> ⓘ
where
Self: Sized,
fn chain<R: Read>(self, next: R) -> Chain<Self, R> ⓘ
where
Self: Sized,
fn take(self, limit: u64) -> Take<Self> ⓘ
where
Self: Sized,
limit
bytes from it. Read more
impl Seek for &File
fn seek(&mut self, pos: SeekFrom) -> Result<u64>
fn rewind(&mut self) -> Result<()>
fn stream_len(&mut self) -> Result<u64>
seek_stream_len
#59359)
fn stream_position(&mut self) -> Result<u64>
impl Seek for File
fn seek(&mut self, pos: SeekFrom) -> Result<u64>
fn rewind(&mut self) -> Result<()>
fn stream_len(&mut self) -> Result<u64>
seek_stream_len
#59359)
fn stream_position(&mut self) -> Result<u64>
impl Write for &File
fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn is_write_vectored(&self) -> bool
can_vector
#69941)
fn flush(&mut self) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)
fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>
fn by_ref(&mut self) -> &mut Self
where
Self: Sized,
Write
. Read more
impl Write for File
fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn is_write_vectored(&self) -> bool
can_vector
#69941)
fn flush(&mut self) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)
fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>
fn by_ref(&mut self) -> &mut Self
where
Self: Sized,
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> Any for T
where
T: 'static + ?Sized,
impl<T> Borrow<T> for T
where
T: ?Sized,
impl<T> BorrowMut<T> for T
where
T: ?Sized,
impl<T> From<T> for T
fn from(t: T) -> T
Returns the argument unchanged.
impl<T, U> Into<U> for T
where
U: From<T>,
fn into(self) -> U
Calls U::from(self)
.
That is, this conversion is whatever the implementation of From<T> for U
chooses to do.
impl<T, U> TryFrom<U> for T
where
U: Into<T>,
type Error = Infallible
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
impl<T, U> TryInto<U> for T
where
U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
© 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