TArray::Empty

function Core Since 4.0

#include "Containers/Array.h"

Access: public

Description

Destructs all elements and sets Num to 0. Reallocates the backing buffer to exactly Slack capacity, releasing excess memory. Use when you want a clean slate and control over post-clear capacity.

Caveats & Gotchas

• Empty(0) frees the entire allocation — subsequent adds will reallocate. If you intend to refill the array immediately, pass the expected new count as Slack to avoid a reallocation: Empty(ExpectedCount).
• Unlike Reset(), Empty() always reallocates to match the requested Slack exactly, even if it means growing the buffer. Reset() only reallocates when it needs to grow.
• Destructors are called on all current elements before any reallocation, so it is safe for elements with non-trivial destructors (FString, TSharedPtr, etc.).

Signature

void Empty(SizeType Slack = 0)

Parameters

Name	Type	Description	Default
Slack	SizeType	Desired capacity to retain after emptying. Pass 0 to release all memory.	0

Return Type

void

Example

Clear and recycle capacity for a known next batch size C++

TArray<FHitResult> HitResults;

void AMyActor::Tick(float DeltaTime)
{
    // Clear results from last frame, but pre-allocate for this frame's expected hits
    HitResults.Empty(32);
    GetWorld()->LineTraceMultiByChannel(HitResults, ...);
}

Version History

Introduced in: 4.0

Version	Status	Notes
5.6	stable	—

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