Error in std::io - Rust (original) (raw)
Struct Error
1.0.0 · Source
pub struct Error { /* private fields */ }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 ofError can be created with crafted error messages and a particular value ofErrorKind.
1.0.0 · Source
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 fromErrorKind.
§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);1.74.0 · Source
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::newwith 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);1.0.0 · Source
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 ofError 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:?}");1.0.0 · Source
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);1.0.0 · Source
Returns the OS error that this error represents (if any).
If this Error was constructed via last_os_error orfrom_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!"));
}1.3.0 · Source
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!"));
}1.3.0 · Source
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())));
}1.3.0 · Source
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!"));
}1.79.0 · Source
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 callingBox<dyn Error + Sync + Send>::downcast on the custom boxed error, returned byError::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 {
// ...
}
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),
}
}
}
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());1.0.0 · Source
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!"));
}👎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
Returns the lower-level source of this error, if any. Read more
🔬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}"));Converts to this type from the input type.
Converts TryReserveError to an error with ErrorKind::OutOfMemory.
TryReserveError won’t be available as the error source(), but this may change in the future.