## `getBlockNumber`

### Signature

```solidity
function getBlockNumber() external view returns (uint256 height);
```

### Description

Gets the current `block.number`.

This cheatcode is particularly useful when using `--via-ir` compilation with `vm.roll`. The Solidity compiler assumes `block.number` is constant during a transaction, so with IR optimization enabled, multiple calls to `block.number` may return the same cached value instead of the updated value. `vm.getBlockNumber()` avoids this optimization and always returns the current `block.number`.

### Returns

| Parameter | Type      | Description                    |
|-----------|-----------|-------------------------------|
| `height`  | `uint256` | The current block number      |

### Examples

```solidity [test/GetBlockNumber.t.sol]
function testGetBlockNumber() public {
    uint256 height = vm.getBlockNumber();
    assertEq(height, block.number);
    vm.roll(10);
    assertEq(vm.getBlockNumber(), 10);
}
```

### Gotchas

:::note
You only need to use this cheatcode when compiling with `--via-ir`. Without IR compilation, accessing `block.number` directly works as expected.
:::

### Related Cheatcodes

* [`roll`](/reference/cheatcodes/roll) - Sets `block.number`
* [`getBlockTimestamp`](/reference/cheatcodes/get-block-timestamp) - Gets the current block timestamp (avoids IR optimization issues)