pub struct File { /* private fields */ }
Expand description
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.
File
does not buffer reads and writes. For efficiency, consider wrapping the
file in a BufReader
or BufWriter
when performing many small read
or write
calls, unless unbuffered reads and writes are required.
§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(())
}
RunRead 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(())
}
RunUsing a buffered Read
er:
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(())
}
RunNote 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§
source§impl File
impl File
sourcepub fn open<P: AsRef<Path>>(path: P) -> Result<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(())
}
Runsourcepub fn create<P: AsRef<Path>>(path: P) -> Result<File>
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(())
}
Run1.77.0 · sourcepub fn create_new<P: AsRef<Path>>(path: P) -> Result<File>
pub fn create_new<P: AsRef<Path>>(path: P) -> Result<File>
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
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(())
}
Run1.58.0 · sourcepub fn options() -> OpenOptions
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(())
}
Runsourcepub fn sync_all(&self) -> Result<()>
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(())
}
Runsourcepub fn sync_data(&self) -> Result<()>
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(())
}
Runsourcepub fn set_len(&self, size: u64) -> Result<()>
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(())
}
RunNote that this method alters the content of the underlying file, even
though it takes &self
rather than &mut self
.
1.9.0 · sourcepub fn try_clone(&self) -> Result<File>
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(())
}
RunAssuming 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(())
}
Run1.16.0 · sourcepub fn set_permissions(&self, perm: Permissions) -> Result<()>
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(())
}
RunNote that this method alters the permissions of the underlying file,
even though it takes &self
rather than &mut self
.
1.75.0 · sourcepub fn set_times(&self, times: FileTimes) -> Result<()>
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(())
}
Run1.75.0 · sourcepub fn set_modified(&self, time: SystemTime) -> Result<()>
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§
1.63.0 · source§impl AsFd for File
impl AsFd for File
source§fn as_fd(&self) -> BorrowedFd<'_>
fn as_fd(&self) -> BorrowedFd<'_>
1.63.0 · source§impl AsHandle for File
Available on Windows only.
impl AsHandle for File
source§fn as_handle(&self) -> BorrowedHandle<'_>
fn as_handle(&self) -> BorrowedHandle<'_>
source§impl AsRawHandle for File
Available on Windows only.
impl AsRawHandle for File
source§fn as_raw_handle(&self) -> RawHandle
fn as_raw_handle(&self) -> RawHandle
1.15.0 · source§impl FileExt for File
Available on Unix only.
impl FileExt for File
source§fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
source§fn read_vectored_at(
&self,
bufs: &mut [IoSliceMut<'_>],
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 moresource§fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize>
fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize>
source§fn write_vectored_at(&self, bufs: &[IoSlice<'_>], 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 moresource§impl FileExt for File
Available on WASI only.
impl FileExt for File
source§fn read_vectored_at(
&self,
bufs: &mut [IoSliceMut<'_>],
offset: u64
) -> Result<usize>
fn read_vectored_at( &self, bufs: &mut [IoSliceMut<'_>], offset: u64 ) -> Result<usize>
wasi_ext
#71213)source§fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> Result<usize>
fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> Result<usize>
wasi_ext
#71213)source§fn tell(&self) -> Result<u64>
fn tell(&self) -> Result<u64>
wasi_ext
#71213)source§fn fdstat_set_flags(&self, flags: u16) -> Result<()>
fn fdstat_set_flags(&self, flags: u16) -> Result<()>
wasi_ext
#71213)source§fn fdstat_set_rights(&self, rights: u64, inheriting: u64) -> Result<()>
fn fdstat_set_rights(&self, rights: u64, inheriting: u64) -> Result<()>
wasi_ext
#71213)source§fn advise(&self, offset: u64, len: u64, advice: u8) -> Result<()>
fn advise(&self, offset: u64, len: u64, advice: u8) -> Result<()>
wasi_ext
#71213)source§fn allocate(&self, offset: u64, len: u64) -> Result<()>
fn allocate(&self, offset: u64, len: u64) -> Result<()>
wasi_ext
#71213)source§fn create_directory<P: AsRef<Path>>(&self, dir: P) -> Result<()>
fn create_directory<P: AsRef<Path>>(&self, dir: P) -> Result<()>
wasi_ext
#71213)source§fn read_link<P: AsRef<Path>>(&self, path: P) -> Result<PathBuf>
fn read_link<P: AsRef<Path>>(&self, path: P) -> Result<PathBuf>
wasi_ext
#71213)source§fn metadata_at<P: AsRef<Path>>(
&self,
lookup_flags: u32,
path: P
) -> Result<Metadata>
fn metadata_at<P: AsRef<Path>>( &self, lookup_flags: u32, path: P ) -> Result<Metadata>
wasi_ext
#71213)source§fn remove_file<P: AsRef<Path>>(&self, path: P) -> Result<()>
fn remove_file<P: AsRef<Path>>(&self, path: P) -> Result<()>
wasi_ext
#71213)source§fn remove_directory<P: AsRef<Path>>(&self, path: P) -> Result<()>
fn remove_directory<P: AsRef<Path>>(&self, path: P) -> Result<()>
wasi_ext
#71213)source§fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
wasi_ext
#71213)1.33.0 · source§fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
buf
from the given offset. Read more1.63.0 · source§impl From<File> for OwnedHandle
Available on Windows only.
impl From<File> for OwnedHandle
source§fn from(file: File) -> OwnedHandle
fn from(file: File) -> OwnedHandle
1.20.0 · source§impl From<File> for Stdio
impl From<File> for Stdio
source§fn from(file: File) -> 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");
Run1.63.0 · source§impl From<OwnedHandle> for File
Available on Windows only.
impl From<OwnedHandle> for File
source§fn from(owned: OwnedHandle) -> Self
fn from(owned: OwnedHandle) -> Self
1.1.0 · source§impl FromRawHandle for File
Available on Windows only.
impl FromRawHandle for File
1.4.0 · source§impl IntoRawFd for File
impl IntoRawFd for File
source§fn into_raw_fd(self) -> RawFd
fn into_raw_fd(self) -> RawFd
1.4.0 · source§impl IntoRawHandle for File
Available on Windows only.
impl IntoRawHandle for File
source§fn into_raw_handle(self) -> RawHandle
fn into_raw_handle(self) -> RawHandle
1.70.0 · source§impl IsTerminal for File
impl IsTerminal for File
source§fn is_terminal(&self) -> bool
fn is_terminal(&self) -> bool
true
if the descriptor/handle refers to a terminal/tty. Read moresource§impl Read for &File
impl Read for &File
source§fn read(&mut self, buf: &mut [u8]) -> Result<usize>
fn read(&mut self, buf: &mut [u8]) -> Result<usize>
source§fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
read
, except that it reads into a slice of buffers. Read moresource§fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)source§fn is_read_vectored(&self) -> bool
fn is_read_vectored(&self) -> bool
can_vector
#69941)source§fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
buf
. Read moresource§fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
buf
. Read more1.6.0 · source§fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
buf
. Read moresource§fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)cursor
. Read moresource§fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
Read
. Read moresource§impl Read for File
impl Read for File
source§fn read(&mut self, buf: &mut [u8]) -> Result<usize>
fn read(&mut self, buf: &mut [u8]) -> Result<usize>
source§fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
read
, except that it reads into a slice of buffers. Read moresource§fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)source§fn is_read_vectored(&self) -> bool
fn is_read_vectored(&self) -> bool
can_vector
#69941)source§fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
buf
. Read moresource§fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
buf
. Read more1.6.0 · source§fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
buf
. Read moresource§fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<()>
read_buf
#78485)cursor
. Read moresource§fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
fn by_ref(&mut self) -> &mut Selfwhere
Self: Sized,
Read
. Read moresource§impl Seek for &File
impl Seek for &File
source§fn seek(&mut self, pos: SeekFrom) -> Result<u64>
fn seek(&mut self, pos: SeekFrom) -> Result<u64>
source§fn stream_len(&mut self) -> Result<u64>
fn stream_len(&mut self) -> Result<u64>
seek_stream_len
#59359)source§impl Seek for File
impl Seek for File
source§fn seek(&mut self, pos: SeekFrom) -> Result<u64>
fn seek(&mut self, pos: SeekFrom) -> Result<u64>
source§fn stream_len(&mut self) -> Result<u64>
fn stream_len(&mut self) -> Result<u64>
seek_stream_len
#59359)source§impl Write for &File
impl Write for &File
source§fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)source§fn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
source§fn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
source§fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)source§impl Write for File
impl Write for File
source§fn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
source§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
can_vector
#69941)source§fn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
source§fn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
source§fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored
#70436)