# CFStreamCreatePairWithSocketToHost(_:_:_:_:_:) Creates readable and writable streams connected to a TCP/IP port of a particular host. ``` func CFStreamCreatePairWithSocketToHost(_ alloc: CFAllocator!, _ host: CFString!, _ port: UInt32, _ readStream: UnsafeMutablePointer?>!, _ writeStream: UnsafeMutablePointer?>!) ``` ## Parameters `alloc` The allocator to use to allocate memory for the `CFReadStream` and `CFWriteStream` objects. Pass `NULL` or [`kCFAllocatorDefault`](/documentation/CoreFoundation/kCFAllocatorDefault) to use the current default allocator. `host` The hostname to which the socket streams should connect. The host can be specified using an IPv4 or IPv6 address or a fully qualified DNS hostname. `port` The TCP port number to which the socket streams should connect. `readStream` Upon return, a readable stream connected to the socket address in `port`. If you pass `NULL`, this 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, a writable stream connected to the socket address in `port`. If you pass `NULL`, this 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, resolve the hostname, or connect to the remote 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)