# CFStreamCreatePairWithSocketToCFHost(_:_:_:_:_:) Creates readable and writable streams connected to a given `CFHost` object. ``` func CFStreamCreatePairWithSocketToCFHost(_ alloc: CFAllocator?, _ host: CFHost, _ port: Int32, _ readStream: UnsafeMutablePointer?>?, _ writeStream: UnsafeMutablePointer?>?) ``` ## Parameters `alloc` The allocator to use to allocate memory for the `CFReadStream` and `CFWriteStream` objects. Pass `NULL` or kCFAllocatorDefault to use the current default allocator. `host` A `CFHost` object to which the streams are connected. If unresolved, the host will be resolved prior to connecting. `port` The TCP port number to which the socket streams should connect. `readStream` Upon return, contains a `CFReadStream` object connected to the host `host` on port `port`, or `NULL` if there is a failure during creation. If you pass `NULL`, the function will not create a readable stream. Ownership follows the [The Create Rule](https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFMemoryMgmt/Concepts/Ownership.html#//apple_ref/doc/uid/20001148-103029). `writeStream` Upon return, contains a `CFWriteStream` object connected to the host `host` on port `port`, or `NULL` if there is a failure during creation. If you pass `NULL`, the function will not create a writable stream. Ownership follows the [The Create Rule](https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFMemoryMgmt/Concepts/Ownership.html#//apple_ref/doc/uid/20001148-103029). ## Discussion The streams do not create a socket or connect to the specified host until you open one of the streams. Most properties are shared by both streams. Setting a shared property for one stream automatically sets the property for the other. --- 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)