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# entry(atHeight:)

Retrieves a block tree entry by its height on the active chain.

```
func entry(atHeight height: Int32) -> BlockTreeEntry?
```

## Parameters

`height`

The block height (`0` for genesis).

## Return Value

The active-chain entry at that height, or `nil` if out of
range.

## Discussion

Returns `nil` for heights greater than [`height`](/documentation/BitcoinKernel/Chain/height) or negative
heights. Note that this is height-on-the-active-chain lookup; use
[`blockTreeEntry(byHash:)`](/documentation/BitcoinKernel/ChainstateManager/blockTreeEntry(byHash:)) to access blocks on
side chains.