Struct std::fs::OpenOptions
1.0.0 · source · pub struct OpenOptions(/* private fields */);
Expand description
Options and flags which can be used to configure how a file is opened.
This builder exposes the ability to configure how a File
is opened and
what operations are permitted on the open file. The File::open
and
File::create
methods are aliases for commonly used options using this
builder.
Generally speaking, when using OpenOptions
, you’ll first call
OpenOptions::new
, then chain calls to methods to set each option, then
call OpenOptions::open
, passing the path of the file you’re trying to
open. This will give you a io::Result
with a File
inside that you
can further operate on.
§Examples
Opening a file to read:
use std::fs::OpenOptions;
let file = OpenOptions::new().read(true).open("foo.txt");
RunOpening a file for both reading and writing, as well as creating it if it doesn’t exist:
use std::fs::OpenOptions;
let file = OpenOptions::new()
.read(true)
.write(true)
.create(true)
.open("foo.txt");
RunImplementations§
source§impl OpenOptions
impl OpenOptions
sourcepub fn write(&mut self, write: bool) -> &mut Self
pub fn write(&mut self, write: bool) -> &mut Self
Sets the option for write access.
This option, when true, will indicate that the file should be
write
-able if opened.
If the file already exists, any write calls on it will overwrite its contents, without truncating it.
§Examples
use std::fs::OpenOptions;
let file = OpenOptions::new().write(true).open("foo.txt");
Runsourcepub fn append(&mut self, append: bool) -> &mut Self
pub fn append(&mut self, append: bool) -> &mut Self
Sets the option for the append mode.
This option, when true, means that writes will append to a file instead
of overwriting previous contents.
Note that setting .write(true).append(true)
has the same effect as
setting only .append(true)
.
For most filesystems, the operating system guarantees that all writes are atomic: no writes get mangled because another process writes at the same time.
One maybe obvious note when using append-mode: make sure that all data
that belongs together is written to the file in one operation. This
can be done by concatenating strings before passing them to write()
,
or using a buffered writer (with a buffer of adequate size),
and calling flush()
when the message is complete.
If a file is opened with both read and append access, beware that after
opening, and after every write, the position for reading may be set at the
end of the file. So, before writing, save the current position (using
seek(SeekFrom::Current(0))
), and restore it before the next read.
§Note
This function doesn’t create the file if it doesn’t exist. Use the
OpenOptions::create
method to do so.
§Examples
use std::fs::OpenOptions;
let file = OpenOptions::new().append(true).open("foo.txt");
Runsourcepub fn truncate(&mut self, truncate: bool) -> &mut Self
pub fn truncate(&mut self, truncate: bool) -> &mut Self
Sets the option for truncating a previous file.
If a file is successfully opened with this option set it will truncate the file to 0 length if it already exists.
The file must be opened with write access for truncate to work.
§Examples
use std::fs::OpenOptions;
let file = OpenOptions::new().write(true).truncate(true).open("foo.txt");
Runsourcepub fn create(&mut self, create: bool) -> &mut Self
pub fn create(&mut self, create: bool) -> &mut Self
Sets the option to create a new file, or open it if it already exists.
In order for the file to be created, OpenOptions::write
or
OpenOptions::append
access must be used.
See also std::fs::write()
for a simple function to
create a file with a given data.
§Examples
use std::fs::OpenOptions;
let file = OpenOptions::new().write(true).create(true).open("foo.txt");
Run1.9.0 · sourcepub fn create_new(&mut self, create_new: bool) -> &mut Self
pub fn create_new(&mut self, create_new: bool) -> &mut Self
Sets the option to create a new file, failing if it already exists.
No file is allowed to exist at the target location, also no (dangling) symlink. In this way, if the call succeeds, the file returned is guaranteed to be new.
This option is useful because it is atomic. Otherwise between checking whether a file exists and creating a new one, the file may have been created by another process (a TOCTOU race condition / attack).
If .create_new(true)
is set, .create()
and .truncate()
are
ignored.
The file must be opened with write or append access in order to create a new file.
§Examples
use std::fs::OpenOptions;
let file = OpenOptions::new().write(true)
.create_new(true)
.open("foo.txt");
Runsourcepub fn open<P: AsRef<Path>>(&self, path: P) -> Result<File>
pub fn open<P: AsRef<Path>>(&self, path: P) -> Result<File>
Opens a file at path
with the options specified by self
.
§Errors
This function will return an error under a number of different
circumstances. Some of these error conditions are listed here, together
with their io::ErrorKind
. The mapping to io::ErrorKind
s is not
part of the compatibility contract of the function.
NotFound
: The specified file does not exist and neithercreate
orcreate_new
is set.NotFound
: One of the directory components of the file path does not exist.PermissionDenied
: The user lacks permission to get the specified access rights for the file.PermissionDenied
: The user lacks permission to open one of the directory components of the specified path.AlreadyExists
:create_new
was specified and the file already exists.InvalidInput
: Invalid combinations of open options (truncate without write access, no access mode set, etc.).
The following errors don’t match any existing io::ErrorKind
at the moment:
- One of the directory components of the specified file path was not, in fact, a directory.
- Filesystem-level errors: full disk, write permission requested on a read-only file system, exceeded disk quota, too many open files, too long filename, too many symbolic links in the specified path (Unix-like systems only), etc.
§Examples
use std::fs::OpenOptions;
let file = OpenOptions::new().read(true).open("foo.txt");
RunTrait Implementations§
source§impl Clone for OpenOptions
impl Clone for OpenOptions
source§fn clone(&self) -> OpenOptions
fn clone(&self) -> OpenOptions
source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresource§impl Debug for OpenOptions
impl Debug for OpenOptions
source§impl OpenOptionsExt for OpenOptions
Available on WASI only.
impl OpenOptionsExt for OpenOptions
source§fn lookup_flags(&mut self, flags: u32) -> &mut OpenOptions
fn lookup_flags(&mut self, flags: u32) -> &mut OpenOptions
wasi_ext
#71213)source§fn directory(&mut self, dir: bool) -> &mut OpenOptions
fn directory(&mut self, dir: bool) -> &mut OpenOptions
wasi_ext
#71213)OpenOptions
must open a directory or not. Read moresource§fn dsync(&mut self, enabled: bool) -> &mut OpenOptions
fn dsync(&mut self, enabled: bool) -> &mut OpenOptions
wasi_ext
#71213)source§fn nonblock(&mut self, enabled: bool) -> &mut OpenOptions
fn nonblock(&mut self, enabled: bool) -> &mut OpenOptions
wasi_ext
#71213)source§fn rsync(&mut self, enabled: bool) -> &mut OpenOptions
fn rsync(&mut self, enabled: bool) -> &mut OpenOptions
wasi_ext
#71213)source§fn sync(&mut self, enabled: bool) -> &mut OpenOptions
fn sync(&mut self, enabled: bool) -> &mut OpenOptions
wasi_ext
#71213)source§fn fs_rights_base(&mut self, rights: u64) -> &mut OpenOptions
fn fs_rights_base(&mut self, rights: u64) -> &mut OpenOptions
wasi_ext
#71213)fs_rights_base
parameter of path_open
. Read moresource§fn fs_rights_inheriting(&mut self, rights: u64) -> &mut OpenOptions
fn fs_rights_inheriting(&mut self, rights: u64) -> &mut OpenOptions
wasi_ext
#71213)fs_rights_inheriting
parameter of path_open
. Read more1.10.0 · source§impl OpenOptionsExt for OpenOptions
Available on Windows only.
impl OpenOptionsExt for OpenOptions
source§fn access_mode(&mut self, access: u32) -> &mut OpenOptions
fn access_mode(&mut self, access: u32) -> &mut OpenOptions
dwDesiredAccess
argument to the call to CreateFile
with the specified value. Read moresource§fn custom_flags(&mut self, flags: u32) -> &mut OpenOptions
fn custom_flags(&mut self, flags: u32) -> &mut OpenOptions
dwFileFlags
argument to the call to
CreateFile2
to the specified value (or combines it with
attributes
and security_qos_flags
to set the dwFlagsAndAttributes
for CreateFile
). Read moresource§fn attributes(&mut self, attributes: u32) -> &mut OpenOptions
fn attributes(&mut self, attributes: u32) -> &mut OpenOptions
dwFileAttributes
argument to the call to CreateFile2
to
the specified value (or combines it with custom_flags
and
security_qos_flags
to set the dwFlagsAndAttributes
for
CreateFile
). Read moresource§fn security_qos_flags(&mut self, flags: u32) -> &mut OpenOptions
fn security_qos_flags(&mut self, flags: u32) -> &mut OpenOptions
dwSecurityQosFlags
argument to the call to CreateFile2
to
the specified value (or combines it with custom_flags
and attributes
to set the dwFlagsAndAttributes
for CreateFile
). Read more