Struct OpenOptions

pub struct OpenOptions(/* private fields */);

A builder for opening files with configurable options.

Files can be opened in read and/or write mode.

The append option opens files in a special writing mode that moves the file cursor to the end of file before every write operation.

It is also possible to truncate the file right after opening, to create a file if it doesn’t exist yet, or to always create a new file with create_new.

Examples

Open a file for reading:

use async_fs::OpenOptions;

let file = OpenOptions::new()
    .read(true)
    .open("a.txt")
    .await?;

Open a file for both reading and writing, and create it if it doesn’t exist yet:

use async_fs::OpenOptions;

let file = OpenOptions::new()
    .read(true)
    .write(true)
    .create(true)
    .open("a.txt")
    .await?;

Implementations

impl OpenOptions

pub fn new() -> OpenOptions

Creates a blank set of options.

All options are initially set to false.

Examples

use async_fs::OpenOptions;

let file = OpenOptions::new()
    .read(true)
    .open("a.txt")
    .await?;

pub fn read(&mut self, read: bool) -> &mut OpenOptions

Configures the option for read mode.

When set to true, this option means the file will be readable after opening.

Examples

use async_fs::OpenOptions;

let file = OpenOptions::new()
    .read(true)
    .open("a.txt")
    .await?;

pub fn write(&mut self, write: bool) -> &mut OpenOptions

Configures the option for write mode.

When set to true, this option means the file will be writable after opening.

If the file already exists, write calls on it will overwrite the previous contents without truncating it.

Examples

use async_fs::OpenOptions;

let file = OpenOptions::new()
    .write(true)
    .open("a.txt")
    .await?;

pub fn append(&mut self, append: bool) -> &mut OpenOptions

Configures the option for append mode.

When set to true, this option means the file will be writable after opening and the file cursor will be moved to the end of file before every write operaiton.

Examples

use async_fs::OpenOptions;

let file = OpenOptions::new()
    .append(true)
    .open("a.txt")
    .await?;

pub fn truncate(&mut self, truncate: bool) -> &mut OpenOptions

Configures the option for truncating the previous file.

When set to true, the file will be truncated to the length of 0 bytes.

The file must be opened in write or append mode for truncation to work.

Examples

use async_fs::OpenOptions;

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

pub fn create(&mut self, create: bool) -> &mut OpenOptions

Configures the option for creating a new file if it doesn’t exist.

When set to true, this option means a new file will be created if it doesn’t exist.

The file must be opened in write or append mode for file creation to work.

Examples

use async_fs::OpenOptions;

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

pub fn create_new(&mut self, create_new: bool) -> &mut OpenOptions

Configures the option for creating a new file or failing if it already exists.

When set to true, this option means a new file will be created, or the open operation will fail if the file already exists.

The file must be opened in write or append mode for file creation to work.

Examples

use async_fs::OpenOptions;

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

pub fn open<P>(&self, path: P) -> impl Future<Output = Result<File, Error>>

where P: AsRef<Path>,

Opens a file with the configured options.

Errors

An error will be returned in the following situations:

• The file does not exist and neither create nor create_new were set.
• The file’s parent directory does not exist.
• The current process lacks permissions to open the file in the configured mode.
• The file already exists and create_new was set.
• Invalid combination of options was used, like truncate was set but write wasn’t, or none of read, write, and append modes was set.
• An OS-level occurred, like too many files are open or the file name is too long.
• Some other I/O error occurred.

Examples

use async_fs::OpenOptions;

let file = OpenOptions::new()
    .read(true)
    .open("a.txt")
    .await?;

Trait Implementations

impl Clone for OpenOptions

fn clone(&self) -> OpenOptions

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for OpenOptions

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

Formats the value using the given formatter.

impl Default for OpenOptions

fn default() -> OpenOptions

Returns the “default value” for a type.

impl OpenOptionsExt for OpenOptions

fn mode(&mut self, mode: u32) -> &mut OpenOptions

Sets the mode bits that a new file will be created with.

fn custom_flags(&mut self, flags: i32) -> &mut OpenOptions

Passes custom flags to the flags argument of open.