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:
Opening a file for both reading and writing, as well as creating it if it doesn’t exist:
Implementations§
source§impl OpenOptions
impl OpenOptions
1.0.0 · sourcepub fn new() -> Self
pub fn new() -> Self
Creates a blank new set of options ready for configuration.
All options are initially set to false
.
§Examples
1.0.0 · sourcepub fn read(&mut self, read: bool) -> &mut Self
pub fn read(&mut self, read: bool) -> &mut Self
Sets the option for read access.
This option, when true, will indicate that the file should be
read
-able if opened.
§Examples
1.0.0 · 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
1.0.0 · sourcepub 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)
.
Append mode guarantees that writes will be positioned at the current end of file,
even when there are other processes or threads appending to the same file. This is
unlike seek(SeekFrom::End(0))
followed by write()
, which
has a race between seeking and writing during which another writer can write, with
our write()
overwriting their data.
Keep in mind that this does not necessarily guarantee that data appended by
different processes or threads does not interleave. The amount of data accepted a
single write()
call depends on the operating system and file system. A
successful write()
is allowed to write only part of the given data, so even if
you’re careful to provide the whole message in a single call to write()
, there
is no guarantee that it will be written out in full. If you rely on the filesystem
accepting the message in a single write, make sure that all data that belongs
together is written in one operation. This can be done by concatenating strings
before passing them to write()
.
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::stream_position
), 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
1.0.0 · sourcepub 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
1.0.0 · sourcepub 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 some given data.
§Examples
1.9.0 · 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.
If a file exists at the target location, creating a new file will fail with AlreadyExists
or another error based on the situation. See OpenOptions::open
for a
non-exhaustive list of likely errors.
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
1.0.0 · sourcepub 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
Trait Implementations§
1.0.0 · source§impl Clone for OpenOptions
impl Clone for OpenOptions
source§fn clone(&self) -> OpenOptions
fn clone(&self) -> OpenOptions
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read more1.0.0 · source§impl Debug for OpenOptions
impl Debug for OpenOptions
1.1.0 · source§impl OpenOptionsExt for OpenOptions
Available on Unix only.
impl OpenOptionsExt for OpenOptions
source§fn mode(&mut self, mode: u32) -> &mut OpenOptions
fn mode(&mut self, mode: u32) -> &mut OpenOptions
source§fn custom_flags(&mut self, flags: i32) -> &mut OpenOptions
fn custom_flags(&mut self, flags: i32) -> &mut 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