Struct OpenOptions

pub struct OpenOptions { /* private fields */ }

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.

Limitations

• Files MUST be opened in either read XOR write mode.
• VEXos does not allow you to open a file configured as read and write at the same time. Doing so will return an error with File::open. This is a fundamental limtiation of the OS.

Examples

Opening a file to read:

use vexide::fs::OpenOptions;

let file = OpenOptions::new().read(true).open("foo.txt");

Opening a file for writing, as well as creating it if it doesn’t exist:

use vexide::fs::OpenOptions;

let file = OpenOptions::new()
            .write(true)
            .create(true)
            .open("foo.txt");

Implementations

impl OpenOptions

pub const fn new() -> OpenOptions

Creates a blank new set of options ready for configuration.

All options are initially set to false.

Examples

use vexide::fs::OpenOptions;

let mut options = OpenOptions::new();
let file = options.read(true).open("foo.txt");

pub const 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

use vexide::fs::OpenOptions;

let file = OpenOptions::new().read(true).open("foo.txt");

pub const 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 vexide::fs::OpenOptions;

let file = OpenOptions::new().write(true).open("foo.txt");

pub const 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().

Note

This function doesn’t create the file if it doesn’t exist. Use the OpenOptions::create method to do so.

Examples

use vexide::fs::OpenOptions;

let file = OpenOptions::new().append(true).open("foo.txt");

pub const 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 vexide::fs::OpenOptions;

let file = OpenOptions::new().write(true).truncate(true).open("foo.txt");

pub const 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 write() for a simple function to create a file with some given data.

Examples

use vexide::fs::OpenOptions;

let file = OpenOptions::new().write(true).create(true).open("foo.txt");

pub const 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. 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.

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 vexide::fs::OpenOptions;

let file = OpenOptions::new().write(true)
                             .create_new(true)
                             .open("foo.txt");

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::ErrorKinds is not part of the compatibility contract of the function.

• NotFound: The specified file does not exist and neither create or create_new is set.
• AlreadyExists: create_new was specified and the file already exists.
• InvalidInput: Invalid combinations of open options (read/write access both specified, truncate without write access, no access mode set, etc.).

The following errors don’t match any existing io::ErrorKind at the moment:

• Filesystem-level errors: full disk, write permission requested on a read-only file system, exceeded disk quota, too many open files, too long filename.

Examples

use vexide::fs::OpenOptions;

let file = OpenOptions::new().read(true).open("foo.txt");

Trait Implementations

impl Clone for OpenOptions

fn clone(&self) -> OpenOptions

Returns a duplicate of the value.

const fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for OpenOptions

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.