1.0.0[−][src]Struct std::fs::File
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:
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(()) }Run
Read the contents of a file into a String
:
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(()) }Run
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(()) }Run
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.
Methods
impl File
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pub fn open<P: AsRef<Path>>(path: P) -> Result<File>
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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(()) }Run
pub fn create<P: AsRef<Path>>(path: P) -> Result<File>
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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(()) }Run
pub fn sync_all(&self) -> Result<()>
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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(()) }Run
pub fn sync_data(&self) -> Result<()>
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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(()) }Run
pub fn set_len(&self, size: u64) -> Result<()>
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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(()) }Run
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>
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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(()) }Run
pub fn try_clone(&self) -> Result<File>
1.9.0[src]
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(()) }Run
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(()) }Run
pub fn set_permissions(&self, perm: Permissions) -> Result<()>
1.16.0[src]
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(()) }Run
Note that this method alters the permissions of the underlying file,
even though it takes &self
rather than &mut self
.
Trait Implementations
impl Read for File
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fn read(&mut self, buf: &mut [u8]) -> Result<usize>
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fn read_vectored(&mut self, bufs: &mut [IoSliceMut]) -> Result<usize>
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unsafe fn initializer(&self) -> Initializer
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fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
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fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
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fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
1.6.0[src]
ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
[src]
Self: Sized,
ⓘImportant traits for Bytes<R>fn bytes(self) -> Bytes<Self> where
Self: Sized,
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Self: Sized,
ⓘImportant traits for Chain<T, U>fn chain<R: Read>(self, next: R) -> Chain<Self, R> where
Self: Sized,
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Self: Sized,
ⓘImportant traits for Take<T>fn take(self, limit: u64) -> Take<Self> where
Self: Sized,
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Self: Sized,
impl<'_> Read for &'_ File
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fn read(&mut self, buf: &mut [u8]) -> Result<usize>
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fn read_vectored(&mut self, bufs: &mut [IoSliceMut]) -> Result<usize>
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unsafe fn initializer(&self) -> Initializer
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fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize>
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fn read_to_string(&mut self, buf: &mut String) -> Result<usize>
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fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
1.6.0[src]
ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
[src]
Self: Sized,
ⓘImportant traits for Bytes<R>fn bytes(self) -> Bytes<Self> where
Self: Sized,
[src]
Self: Sized,
ⓘImportant traits for Chain<T, U>fn chain<R: Read>(self, next: R) -> Chain<Self, R> where
Self: Sized,
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Self: Sized,
ⓘImportant traits for Take<T>fn take(self, limit: u64) -> Take<Self> where
Self: Sized,
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Self: Sized,
impl Write for File
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fn write(&mut self, buf: &[u8]) -> Result<usize>
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fn write_vectored(&mut self, bufs: &[IoSlice]) -> Result<usize>
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fn flush(&mut self) -> Result<()>
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fn write_all(&mut self, buf: &[u8]) -> Result<()>
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fn write_fmt(&mut self, fmt: Arguments) -> Result<()>
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ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
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Self: Sized,
impl<'_> Write for &'_ File
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fn write(&mut self, buf: &[u8]) -> Result<usize>
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fn write_vectored(&mut self, bufs: &[IoSlice]) -> Result<usize>
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fn flush(&mut self) -> Result<()>
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fn write_all(&mut self, buf: &[u8]) -> Result<()>
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fn write_fmt(&mut self, fmt: Arguments) -> Result<()>
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ⓘImportant traits for &'_ mut Ffn by_ref(&mut self) -> &mut Self where
Self: Sized,
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Self: Sized,
impl Seek for File
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fn seek(&mut self, pos: SeekFrom) -> Result<u64>
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fn stream_len(&mut self) -> Result<u64>
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fn stream_position(&mut self) -> Result<u64>
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impl<'_> Seek for &'_ File
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fn seek(&mut self, pos: SeekFrom) -> Result<u64>
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fn stream_len(&mut self) -> Result<u64>
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fn stream_position(&mut self) -> Result<u64>
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impl AsRawFd for File
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impl FromRawFd for File
1.1.0[src]
ⓘImportant traits for Fileunsafe fn from_raw_fd(fd: RawFd) -> File
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impl IntoRawFd for File
1.4.0[src]
fn into_raw_fd(self) -> RawFd
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impl FileExt for File
1.15.0[src]
fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize>
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fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize>
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fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
1.33.0[src]
fn write_all_at(&self, buf: &[u8], offset: u64) -> Result<()>
1.33.0[src]
impl FileExt for File
1.15.0[src]
fn seek_read(&self, buf: &mut [u8], offset: u64) -> Result<usize>
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fn seek_write(&self, buf: &[u8], offset: u64) -> Result<usize>
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impl AsRawHandle for File
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fn as_raw_handle(&self) -> RawHandle
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impl FromRawHandle for File
1.1.0[src]
ⓘImportant traits for Fileunsafe fn from_raw_handle(handle: RawHandle) -> File
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impl IntoRawHandle for File
1.4.0[src]
fn into_raw_handle(self) -> RawHandle
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impl From<File> for Stdio
1.20.0[src]
fn from(file: File) -> Stdio
[src]
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");Run
impl Debug for File
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Auto Trait Implementations
impl UnwindSafe for File
impl RefUnwindSafe for File
impl Unpin for File
impl Send for File
impl Sync for File
Blanket Implementations
impl<T> From<T> for T
[src]
impl<T, U> TryFrom<U> for T where
U: Into<T>,
[src]
U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
[src]
U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
ⓘImportant traits for &'_ mut Ffn borrow_mut(&mut self) -> &mut T
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impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,