Description
Resizes the array to exactly NewNum elements without initialising any newly added memory. Use this when you intend to immediately overwrite every new element, avoiding the cost of zeroing or construction.
Caveats & Gotchas
- • New elements contain indeterminate (garbage) memory — reading any field before writing to it is undefined behaviour. This is intentional for performance-critical paths where you overwrite the data immediately after (e.g. bulk-loading from a file).
- • Unlike SetNum, this does NOT call destructors when shrinking is not required — wait, it does call RemoveAt which destructs. However when growing, constructors are absolutely not called, so do NOT mix this with non-trivially-constructible types unless you placement-new into each slot.
Signature
void SetNumUninitialized(SizeType NewNum, EAllowShrinking AllowShrinking = UE::Core::Private::AllowShrinkingByDefault<AllocatorType>())Parameters
| Name | Type | Description | Default |
|---|---|---|---|
| NewNum | SizeType | The desired number of elements after the call. | — |
| AllowShrinking | EAllowShrinking | Whether to allow the allocator to shrink when the array shrinks. Defaults to the allocator's default behaviour. | UE::Core::Private::AllowShrinkingByDefault<AllocatorType>() |
Return Type
void Example
Resize for bulk binary read C++
TArray<float> Heights;
Heights.SetNumUninitialized(Width * Height); // reserve exact space
Ar.Serialize(Heights.GetData(), Heights.Num() * sizeof(float));Version History
Introduced in: 4.0
| Version | Status | Notes |
|---|---|---|
| 5.6 | stable | — |
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