Struct std::io::Error

pub struct Error { /* fields omitted */ }

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.

Methods

impl Error

pub 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.

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);

pub 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.

Examples

use std::io::Error;

println!("last OS error: {:?}", Error::last_os_error());

pub fn from_raw_os_error(code: i32) -> Error

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);

On Windows:

use std::io;

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

pub fn raw_os_error(&self) -> Option<i32>

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!"));
}

pub fn get_ref(&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!"));
}

pub fn get_mut(&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 {
    fn description(&self) -> &str { &self.v }
}

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())));
}

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

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!"));
}

pub fn kind(&self) -> ErrorKind

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 "No inner error".
    print_error(Error::last_os_error());
    // Will print "Inner error: ...".
    print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
}

Trait Implementations

impl Error for Error

fn description(&self) -> &str

This method is soft-deprecated.

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

Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

The lower-level cause of this error, if any.

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

The lower-level source of this error, if any.

impl Display for Error

fn fmt(&self, fmt: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Debug for Error

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

Formats the value using the given formatter.

impl From<NulError> for Error

fn from(_: NulError) -> Error

Converts a NulError into a io::Error.

impl<W> From<IntoInnerError<W>> for Error

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

Performs the conversion.

impl From<ErrorKind> for Error

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

fn from(kind: ErrorKind) -> Error

Converts an ErrorKind into an Error.

This conversion allocates 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));