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(())
}Read 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(())
}It can be more efficient to read the contents of a file with a buffered
Reader. 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.
Implementations
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(())
}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(())
}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(())
}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(())
}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(())
}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(())
}Note that this method alters the content of the underlying file, even
though it takes &self rather than &mut self.
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(())
}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.
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(())
}Note that this method alters the permissions of the underlying file,
even though it takes &self rather than &mut self.
Trait Implementations
Extracts the raw handle, without taking any ownership.
Reads the exact number of byte required to fill buf from the given offset. Read more
Performs the conversion.
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");Performs the conversion.
Consumes this object, returning the raw underlying file descriptor. Read more
Consumes this object, returning the raw underlying handle. Read more
Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more
Like read, except that it reads into a slice of buffers. 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
Creates an adapter which will chain this stream with another. Read more
Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more
Like read, except that it reads into a slice of buffers. 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
Creates an adapter which will chain this stream with another. 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
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