impl Error

fn new<E>(kind: ErrorKind, error: E) -> Error
where
    E: Into<Box<dyn Error + Send + Sync>>

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.

Note that this function allocates memory on the heap. 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 (and without memory allocation)
let eof_error = Error::from(ErrorKind::UnexpectedEof);

fn other<E>(error: E) -> Error
where
    E: Into<Box<dyn Error + Send + Sync>>

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

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);

fn last_os_error() -> Error

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:?}");

fn from_raw_os_error(code: RawOsError) -> Error

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

Examples

On Linux:

# if cfg!(target_os = "linux") {
use std::io;

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

On Windows:

# if cfg!(windows) {
use std::io;

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

fn raw_os_error(self: &Self) -> Option<RawOsError>

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!"));
}

fn get_ref(self: &Self) -> Option<&dyn Error + Send + Sync + 'static>

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!"));
}

fn get_mut(self: &mut Self) -> Option<&mut dyn Error + Send + Sync + 'static>

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())));
}

fn into_inner(self: Self) -> Option<Box<dyn Error + Send + Sync>>

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

If this Error was constructed via new or other, 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!"));
}

fn downcast<E>(self: Self) -> Result<E, Self>
where
    E: Error + Send + Sync + 'static

Attempts to downcast the custom boxed error to E.

If this Error contains a custom boxed error, then it would attempt downcasting on the boxed error, otherwise it will return Err.

If the custom boxed error has the same type as E, it will return Ok, otherwise it will also return Err.

This method is meant to be a convenience routine for calling Box<dyn Error + Sync + Send>::downcast on the custom boxed error, returned by Error::into_inner.

Examples

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

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

impl fmt::Display for E {
   // ...
#    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
#        todo!()
#    }
}
impl Error for E {}

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

impl From<E> for io::Error {
    fn from(err: E) -> io::Error {
        match err {
            E::Io(io_error) => io_error,
            e => io::Error::new(io::ErrorKind::Other, e),
        }
    }
}

# fn main() {
let e = E::SomeOtherVariant;
// Convert it to an io::Error
let io_error = io::Error::from(e);
// Cast it back to the original variant
let e = E::from(io_error);
assert!(matches!(e, E::SomeOtherVariant));

let io_error = io::Error::from(io::ErrorKind::AlreadyExists);
// Convert it to E
let e = E::from(io_error);
// Cast it back to the original variant
let io_error = io::Error::from(e);
assert_eq!(io_error.kind(), io::ErrorKind::AlreadyExists);
assert!(io_error.get_ref().is_none());
assert!(io_error.raw_os_error().is_none());
# }

fn kind(self: &Self) -> ErrorKind

Returns the corresponding ErrorKind for this error.

This may be a value set by Rust code constructing custom io::Errors, or if this io::Error was sourced from the operating system, it will be a value inferred from the system's error encoding. See last_os_error for more details.

Examples

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

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

fn main() {
    // As no error has (visibly) occurred, this may print anything!
    // It likely prints a placeholder for unidentified (non-)errors.
    print_error(Error::last_os_error());
    // Will print "AddrInUse".
    print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
}

impl Debug for Error

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

impl Display for Error

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

impl Error for Error

fn cause(self: &Self) -> Option<&dyn Error>

fn source(self: &Self) -> Option<&dyn Error + 'static>

impl Freeze for Error

impl From for Error

fn from(_: NulError) -> Error

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

impl From for Error

fn from(kind: ErrorKind) -> Error

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}"));

impl From for Error

fn from(err: TryLockError) -> Error

impl From for Error

fn from(_: TryReserveError) -> Error

Converts TryReserveError to an error with ErrorKind::OutOfMemory.

TryReserveError won't be available as the error source(), but this may change in the future.

impl RefUnwindSafe for Error

impl Send for Error

impl Sync for Error

impl Unpin for Error

impl UnsafeUnpin for Error

impl UnwindSafe for Error

impl<T> Any for Error

fn type_id(self: &Self) -> TypeId

impl<T> Borrow for Error

fn borrow(self: &Self) -> &T

impl<T> BorrowMut for Error

fn borrow_mut(self: &mut Self) -> &mut T

impl<T> From for Error

fn from(t: T) -> T

Returns the argument unchanged.

impl<T> ToString for Error

fn to_string(self: &Self) -> String

impl<T, U> Into for Error

fn into(self: Self) -> U

Calls U::from(self).

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

impl<T, U> TryFrom for Error

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

impl<T, U> TryInto for Error

fn try_into(self: Self) -> Result<U, <U as TryFrom<T>>::Error>

impl<W> From for Error

fn from(iie: IntoInnerError<W>) -> Error