FromUtf8Error in alloc::string - Rust
Description: A possible error value when converting a `String` from a UTF-8 byte vector.

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## FromUtf8Error

# Struct FromUtf8Error

1.36.0 · Source

    pub struct FromUtf8Error { /* private fields */ }

Expand description

A possible error value when converting a `String` from a UTF-8 byte vector.

This type is the error type for the `from_utf8` method on `String`. It is designed in such a way to carefully avoid reallocations: the `into_bytes` method will give back the byte vector that was used in the conversion attempt.

The `Utf8Error` type provided by `std::str` represents an error that may occur when converting a slice of `u8`s to a `&str`. In this sense, it’s an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error` through the `utf8_error` method.

## §Examples

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

    let value = String::from_utf8(bytes);

    assert!(value.is_err());
    assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());

## Implementations§

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### impl FromUtf8Error

1.26.0 · Source

#### pub fn as_bytes(&self) -> &[u8]

Returns a slice of `u8`s bytes that were attempted to convert to a `String`.

##### §Examples

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

    let value = String::from_utf8(bytes);

    assert_eq!(&[0, 159], value.unwrap_err().as_bytes());

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#### pub fn into_utf8_lossy(self) -> String

🔬This is a nightly-only experimental API. (`string_from_utf8_lossy_owned` #129436)

Converts the bytes into a `String` lossily, substituting invalid UTF-8 sequences with replacement characters.

See `String::from_utf8_lossy` for more details on replacement of invalid sequences, and `String::from_utf8_lossy_owned` for the `String` function which corresponds to this function.

This is useful in conjunction with `String::from_utf8` when you need to branch on whether the bytes are valid UTF-8, but still want to recover a lossily converted `String` in the error case. Use `String::from_utf8_lossy_owned` if you always need a lossily converted `String`.

Since the original `String::from_utf8` error records where validation stopped, this method does not need to re-check the already valid prefix of the byte sequence.

##### §Examples

    #![feature(string_from_utf8_lossy_owned)]
    // some invalid bytes
    let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();

    let (output, had_invalid_utf8) = match String::from_utf8(input) {
        Ok(output) => (output, false),
        Err(error) => {
            // The bytes were not valid UTF-8, but we can still recover a string.
            (error.into_utf8_lossy(), true)
        }
    };

    assert_eq!(String::from("Hello �World"), output);
    assert!(had_invalid_utf8);

1.0.0 · Source

#### pub fn into_bytes(self) -> Vec<u8>

Returns the bytes that were attempted to convert to a `String`.

This method is carefully constructed to avoid allocation. It will consume the error, moving out the bytes, so that a copy of the bytes does not need to be made.

##### §Examples

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

    let value = String::from_utf8(bytes);

    assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());

1.0.0 · Source

#### pub fn utf8_error(&self) -> Utf8Error

Fetch a `Utf8Error` to get more details about the conversion failure.

The `Utf8Error` type provided by `std::str` represents an error that may occur when converting a slice of `u8`s to a `&str`. In this sense, it’s an analogue to `FromUtf8Error`. See its documentation for more details on using it.

##### §Examples

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

    let error = String::from_utf8(bytes).unwrap_err().utf8_error();

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

## Trait Implementations§

1.0.0 · Source§

### impl Clone for FromUtf8Error

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#### fn clone(&self) -> FromUtf8Error

Returns a duplicate of the value. Read more
1.0.0 (const: unstable) · Source§

#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
1.0.0 · Source§

### impl Debug for FromUtf8Error

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

Formats the value using the given formatter. Read more
1.0.0 · Source§

### impl Display for FromUtf8Error

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

Formats the value using the given formatter. Read more
1.0.0 · Source§

### impl Eq for FromUtf8Error

1.0.0 · Source§

### impl Error for FromUtf8Error

1.30.0 · Source§

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

Returns the lower-level source of this error, if any. Read more
1.0.0 · Source§

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

👎Deprecated since 1.42.0:

use the Display impl or to_string()

Read more
1.0.0 · Source§

#### 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
1.0.0 · Source§

### impl PartialEq for FromUtf8Error

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#### fn eq(&self, other: &FromUtf8Error) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl StructuralPartialEq for FromUtf8Error

## Auto Trait Implementations§

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### impl Freeze for FromUtf8Error

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### impl RefUnwindSafe for FromUtf8Error

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### impl Send for FromUtf8Error

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### impl Sync for FromUtf8Error

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### impl Unpin for FromUtf8Error

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### impl UnsafeUnpin for FromUtf8Error

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### impl UnwindSafe for FromUtf8Error

## Blanket Implementations§

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### impl<T> Any for T
where 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 T
where 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 T
where 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> CloneToUninit for T
where T: Clone,

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#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit` #126799)
Performs copy-assignment from `self` to `dest`. 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 T
where 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 T
where 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 T
where T: Display + ?Sized,

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

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