# withUnsafeBytes(_:) Calls the given closure with a pointer to the underlying bytes of the array’s contiguous storage. ``` func withUnsafeBytes(_ body: (UnsafeRawBufferPointer) throws -> R) rethrows -> R ``` ## Parameters `body` A closure with an `UnsafeRawBufferPointer` parameter that points to the contiguous storage for the array. If no such storage exists, it is created. If `body` has a return value, that value is also used as the return value for the `withUnsafeBytes(_:)` method. The argument is valid only for the duration of the closure’s execution. ## Return Value The return value, if any, of the `body` closure parameter. ## Discussion The array’s `Element` type must be a *trivial type*, which can be copied with just a bit-for-bit copy without any indirection or reference-counting operations. Generally, native Swift types that do not contain strong or weak references are trivial, as are imported C structs and enums. The following example copies the bytes of the `numbers` array into a buffer of `UInt8`: ``` var numbers: [Int32] = [1, 2, 3] var byteBuffer: [UInt8] = [] numbers.withUnsafeBytes { byteBuffer.append(contentsOf: $0) } // byteBuffer == [1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0] ``` > Note: This example shows the behavior on a little-endian platform. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)