# CFDataGetMutableBytePtr(_:) Returns a pointer to a mutable byte buffer of a CFMutableData object. ``` func CFDataGetMutableBytePtr(_ theData: CFMutableData!) -> UnsafeMutablePointer! ``` ## Parameters `theData` A CFMutableData object. If you pass an immutable CFData object, the behavior is not defined. ## Return Value A pointer to the bytes associated with `theData`. ## Discussion If the length of `theData`‘s data is not zero, this function is guaranteed to return a pointer to a CFMutableData object’s internal bytes. If the length of `theData`’s data *is* zero, this function may or may not return `NULL` dependent upon many factors related to how the object was created (moreover, in this case the function result might change between different releases and on different platforms). --- 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)