# CFDataReplaceBytes(_:_:_:_:) Replaces those bytes in a CFMutableData object that fall within a specified range with other bytes. ``` func CFDataReplaceBytes(_ theData: CFMutableData!, _ range: CFRange, _ newBytes: UnsafePointer!, _ newLength: CFIndex) ``` ## Parameters `theData` A CFMutableData object. If you pass an immutable CFData object, the behavior is not defined. `range` The range of bytes (that is, the starting byte and the number of bytes from that point) to delete from `theData`’s byte buffer. `newBytes` A pointer to the buffer containing the replacement bytes. `newLength` The number of bytes in the byte buffer `newBytes`. ## Discussion --- 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)