---
title: "withUnsafeBytes(_:)"
framework: foundation
role: symbol
role_heading: Instance Method
path: "foundation/contiguousbytes/withunsafebytes(_:)"
---

# withUnsafeBytes(_:)

Calls the given closure with a pointer to the underlying bytes of the type’s contiguous storage.

## Declaration

```swift
func withUnsafeBytes<R>(_ body: (UnsafeRawBufferPointer) throws -> R) rethrows -> R
```

## Parameters

- `body`: A closure with an doc://com.apple.documentation/documentation/Swift/UnsafeRawBufferPointer 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

Return Value The return value, if any, of the body closure parameter.

## Discussion

Discussion The following example copies the bytes from a string encoded using utf8 into a buffer of UInt8: let data = "Hello".data(using: .utf8) var byteBuffer: [UInt8] = [] _ = data?.withUnsafeBytes { buffer in     byteBuffer.append(contentsOf: buffer) }

// byteBuffer = [72, 101, 108, 108, 111]