Struct std::io::Error

1.0.0 · source · []
pub struct Error {
    repr: Repr,
}
Expand description

The error type for I/O operations of the Read, Write, Seek, and associated traits.

Errors mostly originate from the underlying OS, but custom instances of Error can be created with crafted error messages and a particular value of ErrorKind.

Fields

repr: Repr

Implementations

Creates a new I/O error from a known kind of error as well as an arbitrary error payload.

This function is used to generically create I/O errors which do not originate from the OS itself. The error argument is an arbitrary payload which will be contained in this Error.

If no extra payload is required, use the From conversion from ErrorKind.

Examples
use std::io::{Error, ErrorKind};

// errors can be created from strings
let custom_error = Error::new(ErrorKind::Other, "oh no!");

// errors can also be created from other errors
let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);

// creating an error without payload
let eof_error = Error::from(ErrorKind::UnexpectedEof);
Run
🔬This is a nightly-only experimental API. (io_error_other #91946)

Creates a new I/O error from an arbitrary error payload.

This function is used to generically create I/O errors which do not originate from the OS itself. It is a shortcut for Error::new with ErrorKind::Other.

Examples
#![feature(io_error_other)]

use std::io::Error;

// errors can be created from strings
let custom_error = Error::other("oh no!");

// errors can also be created from other errors
let custom_error2 = Error::other(custom_error);
Run

Creates a new I/O error from a known kind of error as well as a constant message.

This function does not allocate.

You should not use this directly, and instead use the const_io_error! macro: io::const_io_error!(ErrorKind::Something, "some_message").

This function should maybe change to from_static_message<const MSG: &'static str>(kind: ErrorKind) in the future, when const generics allow that.

Returns an error representing the last OS error which occurred.

This function reads the value of errno for the target platform (e.g. GetLastError on Windows) and will return a corresponding instance of Error for the error code.

This should be called immediately after a call to a platform function, otherwise the state of the error value is indeterminate. In particular, other standard library functions may call platform functions that may (or may not) reset the error value even if they succeed.

Examples
use std::io::Error;

let os_error = Error::last_os_error();
println!("last OS error: {os_error:?}");
Run

Creates a new instance of an Error from a particular OS error code.

Examples

On Linux:

use std::io;

let error = io::Error::from_raw_os_error(22);
assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
Run

On Windows:

use std::io;

let error = io::Error::from_raw_os_error(10022);
assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
Run

Returns the OS error that this error represents (if any).

If this Error was constructed via last_os_error or from_raw_os_error, then this function will return Some, otherwise it will return None.

Examples
use std::io::{Error, ErrorKind};

fn print_os_error(err: &Error) {
    if let Some(raw_os_err) = err.raw_os_error() {
        println!("raw OS error: {raw_os_err:?}");
    } else {
        println!("Not an OS error");
    }
}

fn main() {
    // Will print "raw OS error: ...".
    print_os_error(&Error::last_os_error());
    // Will print "Not an OS error".
    print_os_error(&Error::new(ErrorKind::Other, "oh no!"));
}
Run

Returns a reference to the inner error wrapped by this error (if any).

If this Error was constructed via new then this function will return Some, otherwise it will return None.

Examples
use std::io::{Error, ErrorKind};

fn print_error(err: &Error) {
    if let Some(inner_err) = err.get_ref() {
        println!("Inner error: {inner_err:?}");
    } else {
        println!("No inner error");
    }
}

fn main() {
    // Will print "No inner error".
    print_error(&Error::last_os_error());
    // Will print "Inner error: ...".
    print_error(&Error::new(ErrorKind::Other, "oh no!"));
}
Run

Returns a mutable reference to the inner error wrapped by this error (if any).

If this Error was constructed via new then this function will return Some, otherwise it will return None.

Examples
use std::io::{Error, ErrorKind};
use std::{error, fmt};
use std::fmt::Display;

#[derive(Debug)]
struct MyError {
    v: String,
}

impl MyError {
    fn new() -> MyError {
        MyError {
            v: "oh no!".to_string()
        }
    }

    fn change_message(&mut self, new_message: &str) {
        self.v = new_message.to_string();
    }
}

impl error::Error for MyError {}

impl Display for MyError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "MyError: {}", &self.v)
    }
}

fn change_error(mut err: Error) -> Error {
    if let Some(inner_err) = err.get_mut() {
        inner_err.downcast_mut::<MyError>().unwrap().change_message("I've been changed!");
    }
    err
}

fn print_error(err: &Error) {
    if let Some(inner_err) = err.get_ref() {
        println!("Inner error: {inner_err}");
    } else {
        println!("No inner error");
    }
}

fn main() {
    // Will print "No inner error".
    print_error(&change_error(Error::last_os_error()));
    // Will print "Inner error: ...".
    print_error(&change_error(Error::new(ErrorKind::Other, MyError::new())));
}
Run

Consumes the Error, returning its inner error (if any).

If this Error was constructed via new then this function will return Some, otherwise it will return None.

Examples
use std::io::{Error, ErrorKind};

fn print_error(err: Error) {
    if let Some(inner_err) = err.into_inner() {
        println!("Inner error: {inner_err}");
    } else {
        println!("No inner error");
    }
}

fn main() {
    // Will print "No inner error".
    print_error(Error::last_os_error());
    // Will print "Inner error: ...".
    print_error(Error::new(ErrorKind::Other, "oh no!"));
}
Run
🔬This is a nightly-only experimental API. (io_error_downcast #99262)

Attempt to downgrade the inner error to E if any.

If this Error was constructed via new then this function will attempt to perform downgrade on it, otherwise it will return Err.

If downgrade succeeds, it will return Ok, otherwise it will also return Err.

Examples
#![feature(io_error_downcast)]

use std::fmt;
use std::io;
use std::error::Error;

#[derive(Debug)]
enum E {
    Io(io::Error),
    SomeOtherVariant,
}

impl fmt::Display for E {
   // ...
}
impl Error for E {}

impl From<io::Error> for E {
    fn from(err: io::Error) -> E {
        err.downcast::<E>()
            .map(|b| *b)
            .unwrap_or_else(E::Io)
    }
}
Run

Returns the corresponding ErrorKind for this error.

Examples
use std::io::{Error, ErrorKind};

fn print_error(err: Error) {
    println!("{:?}", err.kind());
}

fn main() {
    // Will print "Uncategorized".
    print_error(Error::last_os_error());
    // Will print "AddrInUse".
    print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
}
Run

Trait Implementations

Formats the value using the given formatter. Read more
Formats the value using the given formatter. Read more
👎Deprecated since 1.42.0: use the Display impl or to_string()
👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting
The lower-level source of this error, if any. Read more
🔬This is a nightly-only experimental API. (error_type_id #60784)
Gets the TypeId of self.
🔬This is a nightly-only experimental API. (error_generic_member_access #99301)
Provides type based access to context intended for error reports. Read more

Intended for use for errors not exposed to the user, where allocating onto the heap (for normal construction via Error::new) is too costly.

Converts an ErrorKind into an Error.

This conversion creates a new error with a simple representation of error kind.

Examples
use std::io::{Error, ErrorKind};

let not_found = ErrorKind::NotFound;
let error = Error::from(not_found);
assert_eq!("entity not found", format!("{error}"));
Run
Converts to this type from the input type.

Converts a alloc::ffi::NulError into a Error.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

🔬This is a nightly-only experimental API. (provide_any #96024)
Data providers should implement this method to provide all values they are able to provide by using demand. Read more
Converts the given value to a String. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.