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.
Create 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(())
}
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(())
}
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.
Attempts to open a file in read-only mode.
See the OpenOptions::open
method for more details.
This function will return an error if path
does not already exist.
Other errors may also be returned according to OpenOptions::open
.
use std::fs::File;
fn main() -> std::io::Result<()> {
let mut f = File::open("foo.txt")?;
Ok(())
}
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.
use std::fs::File;
fn main() -> std::io::Result<()> {
let mut f = File::create("foo.txt")?;
Ok(())
}
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.
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(())
}
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
.
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(())
}
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.
This function will return an error if the file is not opened for writing.
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
.
Queries metadata about the underlying file.
use std::fs::File;
fn main() -> std::io::Result<()> {
let mut f = File::open("foo.txt")?;
let metadata = f.metadata()?;
Ok(())
}
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.
Create 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(())
}
Changes the permissions on the underlying file.
This function currently corresponds to the fchmod
function on Unix and
the SetFileInformationByHandle
function on Windows. Note that, this
may change in the future.
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.
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
.
Consumes this object, returning the raw underlying file descriptor. Read more
Seek to an offset, in bytes, in a stream. Read more
Seek to an offset, in bytes, in a stream. Read more
Constructs a new instance of Self
from the given raw file descriptor. Read more
Write a buffer into this writer, returning how many bytes were written. Read more
Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
Attempts to write an entire buffer into this writer. Read more
Writes a formatted string into this writer, returning any error encountered. Read more
Creates a "by reference" adaptor for this instance of Write
. Read more
Write a buffer into this writer, returning how many bytes were written. Read more
Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
Attempts to write an entire buffer into this writer. Read more
Writes a formatted string into this writer, returning any error encountered. Read more
Creates a "by reference" adaptor for this instance of Write
. Read more
Reads a number of bytes starting from a given offset. Read more
Writes a number of bytes starting from a given offset. Read more
🔬 This is a nightly-only experimental API. (rw_exact_all_at
)
Reads the exact number of byte required to fill buf
from the given offset. Read more
🔬 This is a nightly-only experimental API. (rw_exact_all_at
)
Attempts to write an entire buffer starting from a given offset. Read more
Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more
🔬 This is a nightly-only experimental API. (read_initializer
)
Determines if this Read
er can work with buffers of uninitialized memory. Read more
Read all bytes until EOF in this source, placing them into buf
. Read more
Read all bytes until EOF in this source, appending them to buf
. Read more
Read the exact number of bytes required to fill buf
. Read more
Creates a "by reference" adaptor for this instance of Read
. Read more
Transforms this Read
instance to an [Iterator
] over its bytes. Read more
Creates an adaptor which will chain this stream with another. Read more
Creates an adaptor which will read at most limit
bytes from it. Read more
Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more
🔬 This is a nightly-only experimental API. (read_initializer
)
Determines if this Read
er can work with buffers of uninitialized memory. Read more
Read all bytes until EOF in this source, placing them into buf
. Read more
Read all bytes until EOF in this source, appending them to buf
. Read more
Read the exact number of bytes required to fill buf
. Read more
Creates a "by reference" adaptor for this instance of Read
. Read more
Transforms this Read
instance to an [Iterator
] over its bytes. Read more
Creates an adaptor which will chain this stream with another. Read more
Creates an adaptor which will read at most limit
bytes from it. Read more
Formats the value using the given formatter. Read more
Converts a File
into a Stdio
File
will be converted to Stdio
using Stdio::from
under the hood.
use std::fs::File;
use std::process::Command;
let file = File::open("foo.txt").unwrap();
let reverse = Command::new("rev")
.stdin(file)
.output()
.expect("failed reverse command");
assert_eq!(reverse.stdout, b"!dlrow ,olleH");
type Error = !
🔬 This is a nightly-only experimental API. (try_from
)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (try_from
)
Immutably borrows from an owned value. Read more
🔬 This is a nightly-only experimental API. (get_type_id
)
this method will likely be replaced by an associated static
type Error = <U as TryFrom<T>>::Error
🔬 This is a nightly-only experimental API. (try_from
)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (try_from
)
Mutably borrows from an owned value. Read more