# CFWriteStreamCreateWithAllocatedBuffers(_:_:) Creates a writable stream for a growable block of memory. ``` func CFWriteStreamCreateWithAllocatedBuffers(_ alloc: CFAllocator!, _ bufferAllocator: CFAllocator!) -> CFWriteStream! ``` ## Parameters `alloc` The allocator to use to allocate memory for the new object. Pass `NULL` or kCFAllocatorDefault to use the current default allocator. `bufferAllocator` The allocator to use to allocate memory for the stream’s memory buffers. Pass `NULL` or kCFAllocatorDefault to use the current default allocator. ## Return Value A new write 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 New buffers are allocated using `bufferAllocator` as bytes are written to the stream. At any point, you can recover the bytes thus far written by asking for the property kCFStreamPropertyDataWritten with [`CFWriteStreamCopyProperty(_:_:)`](/documentation/CoreFoundation/CFWriteStreamCopyProperty(_:_:)). You must open the stream, using [`CFWriteStreamOpen(_:)`](/documentation/CoreFoundation/CFWriteStreamOpen(_:)), before writing to it. --- 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)