# readInto:startingAt:length:completionHandler: Reads data from the resource into a buffer and executes a block afterwards. ``` - (void) readInto:(void *) buffer startingAt:(off_t) offset length:(size_t) length completionHandler:(void (^)(size_t actuallyRead, NSError *error)) completionHandler; ``` ## 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 block 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 `NULL`, 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)