# read(into:startingAt:length:completionHandler:) Reads data from the resource into a buffer and executes a closure afterwards. ``` func read(into buffer: UnsafeMutableRawBufferPointer, startingAt offset: off_t, length: Int, completionHandler: @escaping (Int, (any Error)?) -> Void) ``` ## Parameters `buffer` A buffer to receive the data. `offset` The offset into the resource from which to start reading. `length` A maximum number of bytes to read. The completion handler receives a parameter with the actual number of bytes read. `completionHandler` A closure that executes after the read operation completes. If successful, the first parameter contains the number of bytes actually read. In the case of an error, the second parameter contains a non-`nil` error. This value is `EFAULT` if `buffer` is `nil`, or `errno` if reading from the resource failed. ## Discussion For the read to succeed, requests must conform to any transfer requirements of the underlying resource. Disk drives typically require sector (`physicalBlockSize`) addressed operations of one or more sector-aligned offsets. --- 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)