# replaceBytes(in:withBytes:length:) Replaces with a given set of bytes a given range within the contents of the receiver. ``` func replaceBytes(in range: NSRange, withBytes replacementBytes: UnsafeRawPointer?, length replacementLength: Int) ``` ## Parameters `range` The range within the receiver’s contents to replace with `bytes`. The range must not exceed the bounds of the receiver. `replacementBytes` The data to insert into the receiver’s contents. `replacementLength` The number of bytes to take from `replacementBytes`. ## Discussion If the length of `range` is not equal to `replacementLength`, the receiver is resized to accommodate the new bytes. Any bytes past `range` in the receiver are shifted to accommodate the new bytes. You can therefore pass `NULL` for `replacementBytes` and `0` for `replacementLength` to delete bytes in the receiver in the range `range`. You can also replace a range (which might be zero-length) with more bytes than the length of the range, which has the effect of insertion (or “replace some and insert more”). --- 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)