<!--
{
  "documentType" : "article",
  "framework" : "CoreFoundation",
  "identifier" : "/documentation/CoreFoundation/1477595-callback-identifiers",
  "metadataVersion" : "0.1.0",
  "role" : "collectionGroup",
  "title" : "Callback Identifiers"
}
-->

# Callback Identifiers

Constants that identify the read and write callbacks.

## Topics

### Constants

[`var kCFFileDescriptorReadCallBack: CFOptionFlags`](/documentation/CoreFoundation/kCFFileDescriptorReadCallBack)

Identifies the read callback.

[`var kCFFileDescriptorWriteCallBack: CFOptionFlags`](/documentation/CoreFoundation/kCFFileDescriptorWriteCallBack)

Identifies the write callback.


---

Copyright &copy; 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)