Struct funk::fs::File 1.0.0
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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.
Examples
Create a new file and write bytes to it:
use std::fs::File; use std::io::prelude::*; let mut file = File::create("foo.txt")?; file.write_all(b"Hello, world!")?;
Read the contents of a file into a String
:
use std::fs::File; use std::io::prelude::*; let mut file = File::open("foo.txt")?; let mut contents = String::new(); file.read_to_string(&mut contents)?; assert_eq!(contents, "Hello, world!");
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::*; 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!");
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>(path: P) -> Result<File, Error> where
P: AsRef<Path>,
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P: AsRef<Path>,
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; let mut f = File::open("foo.txt")?;
pub fn create<P>(path: P) -> Result<File, Error> where
P: AsRef<Path>,
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P: AsRef<Path>,
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; let mut f = File::create("foo.txt")?;
pub fn sync_all(&self) -> Result<(), Error>
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Attempts to sync all OS-internal metadata to disk.
This function will attempt to ensure that all in-core data reaches the filesystem before returning.
Examples
use std::fs::File; use std::io::prelude::*; let mut f = File::create("foo.txt")?; f.write_all(b"Hello, world!")?; f.sync_all()?;
pub fn sync_data(&self) -> Result<(), Error>
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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::*; let mut f = File::create("foo.txt")?; f.write_all(b"Hello, world!")?; f.sync_data()?;
pub fn set_len(&self, size: u64) -> Result<(), Error>
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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.
Examples
use std::fs::File; let mut f = File::create("foo.txt")?; f.set_len(10)?;
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, Error>
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Queries metadata about the underlying file.
Examples
use std::fs::File; let mut f = File::open("foo.txt")?; let metadata = f.metadata()?;
pub fn try_clone(&self) -> Result<File, Error>
1.9.0[src]
Create 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
Create two handles for a file named foo.txt
:
use std::fs::File; let mut file = File::open("foo.txt")?; let file_copy = file.try_clone()?;
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::*; 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");
pub fn set_permissions(&self, perm: Permissions) -> Result<(), Error>
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
use std::fs::File; let file = File::open("foo.txt")?; let mut perms = file.metadata()?.permissions(); perms.set_readonly(true); file.set_permissions(perms)?;
Note that this method alters the permissions of the underlying file,
even though it takes &self
rather than &mut self
.
Trait Implementations
impl Seek for File
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fn seek(&mut self, pos: SeekFrom) -> Result<u64, Error>
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Seek to an offset, in bytes, in a stream. Read more
impl<'a> Seek for &'a File
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fn seek(&mut self, pos: SeekFrom) -> Result<u64, Error>
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Seek to an offset, in bytes, in a stream. Read more
impl<'a> Write for &'a File
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fn write(&mut self, buf: &[u8]) -> Result<usize, Error>
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Write a buffer into this object, returning how many bytes were written. Read more
fn flush(&mut self) -> Result<(), Error>
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Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>
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Attempts to write an entire buffer into this write. Read more
fn write_fmt(&mut self, fmt: Arguments) -> Result<(), Error>
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Writes a formatted string into this writer, returning any error encountered. Read more
ⓘImportant traits for &'a mut Wfn by_ref(&mut self) -> &mut Self
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Creates a "by reference" adaptor for this instance of Write
. Read more
impl Write for File
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fn write(&mut self, buf: &[u8]) -> Result<usize, Error>
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Write a buffer into this object, returning how many bytes were written. Read more
fn flush(&mut self) -> Result<(), Error>
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Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>
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Attempts to write an entire buffer into this write. Read more
fn write_fmt(&mut self, fmt: Arguments) -> Result<(), Error>
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Writes a formatted string into this writer, returning any error encountered. Read more
ⓘImportant traits for &'a mut Wfn by_ref(&mut self) -> &mut Self
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Creates a "by reference" adaptor for this instance of Write
. Read more
impl IntoRawFd for File
1.4.0[src]
fn into_raw_fd(self) -> i32
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Consumes this object, returning the raw underlying file descriptor. Read more
impl Debug for File
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fn fmt(&self, f: &mut Formatter) -> Result<(), Error>
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Formats the value using the given formatter. Read more
impl FromRawFd for File
1.1.0[src]
ⓘImportant traits for &'a Fileunsafe fn from_raw_fd(fd: i32) -> File
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Constructs a new instance of Self
from the given raw file descriptor. Read more
impl FileExt for File
1.15.0[src]
fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<usize, Error>
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Reads a number of bytes starting from a given offset. Read more
fn write_at(&self, buf: &[u8], offset: u64) -> Result<usize, Error>
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Writes a number of bytes starting from a given offset. Read more
impl From<File> for Stdio
1.20.0[src]
impl AsRawFd for File
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impl<'a> Read for &'a File
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fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error>
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Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more
unsafe fn initializer(&self) -> Initializer
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read_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, Error>
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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, Error>
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Read all bytes until EOF in this source, appending them to buf
. Read more
fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>
1.6.0[src]
Read the exact number of bytes required to fill buf
. Read more
ⓘImportant traits for &'a mut Wfn by_ref(&mut self) -> &mut Self
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Creates a "by reference" adaptor for this instance of Read
. Read more
ⓘImportant traits for Bytes<R>fn bytes(self) -> Bytes<Self>
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Transforms this Read
instance to an [Iterator
] over its bytes. Read more
ⓘImportant traits for Chars<R>fn chars(self) -> Chars<Self>
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🔬 This is a nightly-only experimental API. (io
)
the semantics of a partial read/write of where errors happen is currently unclear and may change
Transforms this Read
instance to an [Iterator
] over [char
]s. Read more
ⓘImportant traits for Chain<T, U>fn chain<R>(self, next: R) -> Chain<Self, R> where
R: Read,
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R: Read,
Creates an adaptor which will chain this stream with another. Read more
ⓘImportant traits for Take<T>fn take(self, limit: u64) -> Take<Self>
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Creates an adaptor which will read at most limit
bytes from it. Read more
impl Read for File
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fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error>
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Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more
unsafe fn initializer(&self) -> Initializer
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read_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, Error>
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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, Error>
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Read all bytes until EOF in this source, appending them to buf
. Read more
fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>
1.6.0[src]
Read the exact number of bytes required to fill buf
. Read more
ⓘImportant traits for &'a mut Wfn by_ref(&mut self) -> &mut Self
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Creates a "by reference" adaptor for this instance of Read
. Read more
ⓘImportant traits for Bytes<R>fn bytes(self) -> Bytes<Self>
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Transforms this Read
instance to an [Iterator
] over its bytes. Read more
ⓘImportant traits for Chars<R>fn chars(self) -> Chars<Self>
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🔬 This is a nightly-only experimental API. (io
)
the semantics of a partial read/write of where errors happen is currently unclear and may change
Transforms this Read
instance to an [Iterator
] over [char
]s. Read more
ⓘImportant traits for Chain<T, U>fn chain<R>(self, next: R) -> Chain<Self, R> where
R: Read,
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R: Read,
Creates an adaptor which will chain this stream with another. Read more
ⓘImportant traits for Take<T>fn take(self, limit: u64) -> Take<Self>
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Creates an adaptor which will read at most limit
bytes from it. Read more