# withUnsafeBytes(_:) Calls the given closure with a pointer to the underlying bytes of the type’s contiguous storage. ``` func withUnsafeBytes(_ body: (UnsafeRawBufferPointer) throws -> R) rethrows -> R ``` ## Parameters `body` A closure with an parameter that points to the contiguous storage for the type. If no such storage exists, the method creates it. If `body` has a return value, this method also returns that value. 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 following example copies the bytes from a string encoded using `utf8` into a buffer of `UInt8`: ```swift let data = "Hello".data(using: .utf8) var byteBuffer: [UInt8] = [] _ = data?.withUnsafeBytes { buffer in byteBuffer.append(contentsOf: buffer) } // byteBuffer = [72, 101, 108, 108, 111] ``` --- 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)