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

# withUnsafeBytes(_:)

Calls the given closure with a pointer to the underlying bytes of the viewed contiguous storage.

## Declaration

```swift
func withUnsafeBytes<E, Result>(_ body: (UnsafeRawBufferPointer) throws(E) -> Result) throws(E) -> Result where E : Error, Result : ~Copyable
```

## Parameters

- `body`: A closure with an UnsafeRawBufferPointer parameter that points to the viewed contiguous storage. If body has a return value, that value is also used as the return value for the withUnsafeBytes(_:) method. The closure’s parameter is valid only for the duration of its execution.

## Return Value

Return Value The return value of the body closure parameter.

## Discussion

Discussion The buffer pointer passed as an argument to body is valid only during the execution of withUnsafeBytes(_:). Do not store or return the pointer for later use. Note: For an empty RawSpan, the closure always receives a nil pointer.