# Struct std::os::windows::io::HandleOrNull

1.63.0 · source ·

    pub struct HandleOrNull(/* private fields */);

Available on Windows only.
Expand description

FFI type for handles in return values or out parameters, where `NULL` is used as a sentry value to indicate errors, such as in the return value of `CreateThread`. This uses `repr(transparent)` and has the representation of a host handle, so that it can be used in such FFI declarations.

The only thing you can usefully do with a `HandleOrNull` is to convert it into an `OwnedHandle` using its `TryFrom` implementation; this conversion takes care of the check for `NULL`. This ensures that such FFI calls cannot start using the handle without checking for `NULL` first.

This type may hold any handle value that `OwnedHandle` may hold. As with `OwnedHandle`, when it holds `-1`, that value is interpreted as a valid handle value, such as the current process handle, and not `INVALID_HANDLE_VALUE`.

If this holds a non-null handle, it will close the handle on drop.

## Implementations§

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### impl HandleOrNull

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#### pub unsafe fn from_raw_handle(handle: RawHandle) -> Self

Constructs a new instance of `Self` from the given `RawHandle` returned from a Windows API that uses null to indicate failure, such as `CreateThread`.

Use `HandleOrInvalid` instead of `HandleOrNull` for APIs that use `INVALID_HANDLE_VALUE` to indicate failure.

##### Safety

The passed `handle` value must either satisfy the safety requirements of `FromRawHandle::from_raw_handle`, or be null. Note that not all Windows APIs use null for errors; see here for the full story.

## Trait Implementations§

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### impl Debug for HandleOrNull

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

Formats the value using the given formatter. Read more
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### impl TryFrom<HandleOrNull> for OwnedHandle

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#### type Error = NullHandleError

The type returned in the event of a conversion error.
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#### fn try_from(handle_or_null: HandleOrNull) -> Result<Self, NullHandleError>

Performs the conversion.
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### impl Send for HandleOrNull

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### impl Sync for HandleOrNull

## Auto Trait Implementations§

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### impl RefUnwindSafe for HandleOrNull

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### impl Unpin for HandleOrNull

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### impl UnwindSafe for HandleOrNull

## 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, 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.