pub struct File { /* private fields */ }
Expand description
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(())
}
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(())
}
RunIt 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(())
}
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
sourceimpl 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.
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(())
}
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.
Examples
use std::fs::File;
fn main() -> std::io::Result<()> {
let mut f = File::create("foo.txt")?;
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;
fn main() -> std::io::Result<()> {
let mut f = File::options().append(true).open("example.log")?;
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
.
Trait Implementations
1.63.0 · sourceimpl AsFd for File
impl AsFd for File
sourcefn as_fd(&self) -> BorrowedFd<'_>
fn as_fd(&self) -> BorrowedFd<'_>
Borrows the file descriptor. Read more
1.63.0 · sourceimpl AsHandle for File
Available on Windows only.
impl AsHandle for File
sourcefn as_handle(&self) -> BorrowedHandle<'_>
fn as_handle(&self) -> BorrowedHandle<'_>
Borrows the handle. Read more
sourceimpl AsRawHandle for File
Available on Windows only.
impl AsRawHandle for File
sourcefn as_raw_handle(&self) -> RawHandle
fn as_raw_handle(&self) -> RawHandle
Extracts the raw handle. Read more
1.15.0 · sourceimpl FileExt for File
Available on Unix only.
impl FileExt for File
sourcefn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
Reads a number of bytes starting from a given offset. Read more
sourcefn write_at(&self, buf: &[u8], offset: u64) -> Result<usize>
fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize>
Writes a number of bytes starting from a given offset. Read more
sourceimpl FileExt for File
Available on WASI only.
impl FileExt for File
sourcefn read_vectored_at(
&self,
bufs: &mut [IoSliceMut<'_>],
offset: u64
) -> Result<usize>
fn read_vectored_at(
&self,
bufs: &mut [IoSliceMut<'_>],
offset: u64
) -> Result<usize>
Reads a number of bytes starting from a given offset. Read more
sourcefn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> Result<usize>
fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> Result<usize>
Writes a number of bytes starting from a given offset. Read more
sourcefn fdstat_set_flags(&self, flags: u16) -> Result<()>
fn fdstat_set_flags(&self, flags: u16) -> Result<()>
Adjust the flags associated with this file. Read more
sourcefn fdstat_set_rights(&self, rights: u64, inheriting: u64) -> Result<()>
fn fdstat_set_rights(&self, rights: u64, inheriting: u64) -> Result<()>
Adjust the rights associated with this file. Read more
sourcefn advise(&self, offset: u64, len: u64, advice: u8) -> Result<()>
fn advise(&self, offset: u64, len: u64, advice: u8) -> Result<()>
Provide file advisory information on a file descriptor. Read more
sourcefn allocate(&self, offset: u64, len: u64) -> Result<()>
fn allocate(&self, offset: u64, len: u64) -> Result<()>
Force the allocation of space in a file. Read more
sourcefn read_link<P: AsRef<Path>>(&self, path: P) -> Result<PathBuf>
fn read_link<P: AsRef<Path>>(&self, path: P) -> Result<PathBuf>
Read the contents of a symbolic link. Read more
sourcefn 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>
Return the attributes of a file or directory. Read more
sourcefn remove_directory<P: AsRef<Path>>(&self, path: P) -> Result<()>
fn remove_directory<P: AsRef<Path>>(&self, path: P) -> Result<()>
Remove a directory. Read more
sourcefn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
Reads a number of bytes starting from a given offset. Read more
1.33.0 · sourcefn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
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
1.63.0 · sourceimpl From<File> for OwnedHandle
Available on Windows only.
impl From<File> for OwnedHandle
sourcefn from(file: File) -> OwnedHandle
fn from(file: File) -> OwnedHandle
Converts to this type from the input type.
1.20.0 · sourceimpl From<File> for Stdio
impl From<File> for Stdio
sourcefn 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 · sourceimpl From<OwnedHandle> for File
Available on Windows only.
impl From<OwnedHandle> for File
sourcefn from(owned: OwnedHandle) -> Self
fn from(owned: OwnedHandle) -> Self
Converts to this type from the input type.
1.1.0 · sourceimpl FromRawHandle for File
Available on Windows only.
impl FromRawHandle for File
1.4.0 · sourceimpl IntoRawFd for File
impl IntoRawFd for File
sourcefn into_raw_fd(self) -> RawFd
fn into_raw_fd(self) -> RawFd
Consumes this object, returning the raw underlying file descriptor. Read more
1.4.0 · sourceimpl IntoRawHandle for File
Available on Windows only.
impl IntoRawHandle for File
sourcefn into_raw_handle(self) -> RawHandle
fn into_raw_handle(self) -> RawHandle
Consumes this object, returning the raw underlying handle. Read more
sourceimpl Read for &File
impl Read for &File
sourcefn read(&mut self, buf: &mut [u8]) -> Result<usize>
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
sourcefn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()>
fn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()>
Pull some bytes from this source into the specified buffer. Read more
sourcefn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
Like read
, except that it reads into a slice of buffers. Read more
sourcefn is_read_vectored(&self) -> bool
fn is_read_vectored(&self) -> bool
Determines if this Read
er has an efficient read_vectored
implementation. Read more
sourcefn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
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
sourcefn read_to_string(&mut self, buf: &mut String) -> Result<usize>
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
1.6.0 · sourcefn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
Read the exact number of bytes required to fill buf
. Read more
sourcefn read_buf_exact(&mut self, buf: &mut ReadBuf<'_>) -> Result<()>
fn read_buf_exact(&mut self, buf: &mut ReadBuf<'_>) -> Result<()>
Read the exact number of bytes required to fill buf
. Read more
sourcefn by_ref(&mut self) -> &mut Self where
Self: Sized,
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
Creates a “by reference” adaptor for this instance of Read
. Read more
sourcefn bytes(self) -> Bytes<Self>ⓘNotable traits for Bytes<R>impl<R: Read> Iterator for Bytes<R> type Item = Result<u8>;
where
Self: Sized,
fn bytes(self) -> Bytes<Self>ⓘNotable traits for Bytes<R>impl<R: Read> Iterator for Bytes<R> type Item = Result<u8>;
where
Self: Sized,
sourceimpl Read for File
impl Read for File
sourcefn read(&mut self, buf: &mut [u8]) -> Result<usize>
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
sourcefn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize>
Like read
, except that it reads into a slice of buffers. Read more
sourcefn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()>
fn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()>
Pull some bytes from this source into the specified buffer. Read more
sourcefn is_read_vectored(&self) -> bool
fn is_read_vectored(&self) -> bool
Determines if this Read
er has an efficient read_vectored
implementation. Read more
sourcefn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
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
sourcefn read_to_string(&mut self, buf: &mut String) -> Result<usize>
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
1.6.0 · sourcefn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
Read the exact number of bytes required to fill buf
. Read more
sourcefn read_buf_exact(&mut self, buf: &mut ReadBuf<'_>) -> Result<()>
fn read_buf_exact(&mut self, buf: &mut ReadBuf<'_>) -> Result<()>
Read the exact number of bytes required to fill buf
. Read more
sourcefn by_ref(&mut self) -> &mut Self where
Self: Sized,
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
Creates a “by reference” adaptor for this instance of Read
. Read more
sourcefn bytes(self) -> Bytes<Self>ⓘNotable traits for Bytes<R>impl<R: Read> Iterator for Bytes<R> type Item = Result<u8>;
where
Self: Sized,
fn bytes(self) -> Bytes<Self>ⓘNotable traits for Bytes<R>impl<R: Read> Iterator for Bytes<R> type Item = Result<u8>;
where
Self: Sized,
sourceimpl Seek for &File
impl Seek for &File
sourcefn seek(&mut self, pos: SeekFrom) -> Result<u64>
fn seek(&mut self, pos: SeekFrom) -> Result<u64>
Seek to an offset, in bytes, in a stream. Read more
sourcefn stream_len(&mut self) -> Result<u64>
fn stream_len(&mut self) -> Result<u64>
Returns the length of this stream (in bytes). Read more
1.51.0 · sourcefn stream_position(&mut self) -> Result<u64>
fn stream_position(&mut self) -> Result<u64>
Returns the current seek position from the start of the stream. Read more
sourceimpl Seek for File
impl Seek for File
sourcefn seek(&mut self, pos: SeekFrom) -> Result<u64>
fn seek(&mut self, pos: SeekFrom) -> Result<u64>
Seek to an offset, in bytes, in a stream. Read more
sourcefn stream_len(&mut self) -> Result<u64>
fn stream_len(&mut self) -> Result<u64>
Returns the length of this stream (in bytes). Read more
1.51.0 · sourcefn stream_position(&mut self) -> Result<u64>
fn stream_position(&mut self) -> Result<u64>
Returns the current seek position from the start of the stream. Read more
sourceimpl Write for &File
impl Write for &File
sourcefn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
Write a buffer into this writer, returning how many bytes were written. Read more
sourcefn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
sourcefn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
Determines if this Write
r has an efficient write_vectored
implementation. Read more
sourcefn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
sourcefn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
Attempts to write an entire buffer into this writer. Read more
sourcefn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
Attempts to write multiple buffers into this writer. Read more
sourceimpl Write for File
impl Write for File
sourcefn write(&mut self, buf: &[u8]) -> Result<usize>
fn write(&mut self, buf: &[u8]) -> Result<usize>
Write a buffer into this writer, returning how many bytes were written. Read more
sourcefn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize>
sourcefn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
Determines if this Write
r has an efficient write_vectored
implementation. Read more
sourcefn flush(&mut self) -> Result<()>
fn flush(&mut self) -> Result<()>
Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
sourcefn write_all(&mut self, buf: &[u8]) -> Result<()>
fn write_all(&mut self, buf: &[u8]) -> Result<()>
Attempts to write an entire buffer into this writer. Read more
sourcefn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
Attempts to write multiple buffers into this writer. 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
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more