# Struct alloc::str::Utf8Error

1.0.0 · source ·

    pub struct Utf8Error { /* private fields */ }

Expand description

Errors which can occur when attempting to interpret a sequence of `u8` as a string.

As such, the `from_utf8` family of functions and methods for both `String`s and `&str`s make use of this error, for example.

## Examples

This error type’s methods can be used to create functionality similar to `String::from_utf8_lossy` without allocating heap memory:

    fn from_utf8_lossy<F>(mut input: &[u8], mut push: F) where F: FnMut(&str) {
        loop {
            match std::str::from_utf8(input) {
                Ok(valid) => {
                    push(valid);
                    break
                }
                Err(error) => {
                    let (valid, after_valid) = input.split_at(error.valid_up_to());
                    unsafe {
                        push(std::str::from_utf8_unchecked(valid))
                    }
                    push("\u{FFFD}");

                    if let Some(invalid_sequence_length) = error.error_len() {
                        input = &after_valid[invalid_sequence_length..]
                    } else {
                        break
                    }
                }
            }
        }
    }

Run

## Implementations§

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### impl Utf8Error

1.5.0 (const: 1.63.0) · source

#### pub const fn valid_up_to(&self) -> usize

Returns the index in the given string up to which valid UTF-8 was verified.

It is the maximum index such that `from_utf8(&input[..index])` would return `Ok(_)`.

##### Examples

Basic usage:

    use std::str;

    // some invalid bytes, in a vector
    let sparkle_heart = vec![0, 159, 146, 150];

    // std::str::from_utf8 returns a Utf8Error
    let error = str::from_utf8(&sparkle_heart).unwrap_err();

    // the second byte is invalid here
    assert_eq!(1, error.valid_up_to());

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1.20.0 (const: 1.63.0) · source

#### pub const fn error_len(&self) -> Option<usize>

Provides more information about the failure:

- `None`: the end of the input was reached unexpectedly. `self.valid_up_to()` is 1 to 3 bytes from the end of the input. If a byte stream (such as a file or a network socket) is being decoded incrementally, this could be a valid `char` whose UTF-8 byte sequence is spanning multiple chunks.

- `Some(len)`: an unexpected byte was encountered. The length provided is that of the invalid byte sequence that starts at the index given by `valid_up_to()`. Decoding should resume after that sequence (after inserting a `U+FFFD REPLACEMENT CHARACTER`) in case of lossy decoding.

## Trait Implementations§

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### impl Clone for Utf8Error

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#### fn clone(&self) -> Utf8Error

Returns a copy of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl Debug for Utf8Error

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

Formats the value using the given formatter. Read more
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### impl Display for Utf8Error

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

Formats the value using the given formatter. Read more
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### impl Error for Utf8Error

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#### fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()
Read more
1.30.0 · source§

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

The lower-level source of this error, if any. Read more
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#### fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting
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#### fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (`error_generic_member_access` #99301)
Provides type based access to context intended for error reports. Read more
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### impl PartialEq for Utf8Error

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#### fn eq(&self, other: &Utf8Error) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Rhs) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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### impl Copy for Utf8Error

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### impl Eq for Utf8Error

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### impl StructuralEq for Utf8Error

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### impl StructuralPartialEq for Utf8Error

## Auto Trait Implementations§

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### impl RefUnwindSafe for Utf8Error

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### impl Send for Utf8Error

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### impl Sync for Utf8Error

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### impl Unpin for Utf8Error

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### impl UnwindSafe for Utf8Error

## Blanket Implementations§

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### impl<T> Any for Twhere T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for Twhere T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for Twhere T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for Twhere U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

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

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### impl<T> ToOwned for Twhere T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T> ToString for Twhere T: Display + ?Sized,

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#### default fn to_string(&self) -> String

Converts the given value to a `String`. Read more
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### impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.