CFWriteStream provides an interface for writing a byte stream either synchronously or asynchronously. You can create streams that write bytes to a block of memory, a file, or a generic socket. All streams need to be opened, using CFWriteStreamOpen(_:), before writing.

Use CFReadStream for reading byte streams, and for the functions, such as CFStreamCreatePairWithSocketToHost(_:_:_:_:_:), that create socket streams).

CFWriteStream is “toll-free bridged” with its Cocoa Foundation counterpart, OutputStream. This means that the Core Foundation type is interchangeable in function or method calls with the bridged Foundation object. Therefore, in a method where you see an NSOutputStream * parameter, you can pass in a CFWriteStreamRef, and in a function where you see a CFWriteStreamRef parameter, you can pass in an NSOutputStream instance. Note, however, that you may have either a delegate or callbacks but not both. See Toll-Free Bridged Types for more information on toll-free bridging.


Creating a Write Stream

func CFWriteStreamCreateWithAllocatedBuffers(CFAllocator!, CFAllocator!)

Creates a writable stream for a growable block of memory.

func CFWriteStreamCreateWithBuffer(CFAllocator!, UnsafeMutablePointer<UInt8>!, CFIndex)

Creates a writable stream for a fixed-size block of memory.

func CFWriteStreamCreateWithFile(CFAllocator!, CFURL!)

Creates a writable stream for a file.

Opening and Closing a Stream

func CFWriteStreamOpen(CFWriteStream!)

Opens a stream for writing.

Writing to a Stream

Examining Stream Properties

func CFWriteStreamCanAcceptBytes(CFWriteStream!)

Returns whether a writable stream can accept new data without blocking.

func CFWriteStreamCopyError(CFWriteStream!)

Returns the error associated with a stream.

func CFWriteStreamGetError(CFWriteStream!)

Returns the error status of a stream.

func CFWriteStreamGetStatus(CFWriteStream!)

Returns the current state of a stream.

Setting Stream Properties

Getting the CFWriteStream Type ID

func CFWriteStreamGetTypeID()

Returns the type identifier of all CFWriteStream objects.


typealias CFWriteStreamClientCallBack

Callback invoked when certain types of activity takes place on a writable stream.

Data Types

class CFWriteStream

A reference to a writable stream object.

See Also

Opaque Types


The CFFileDescriptor provides an opaque type to monitor file descriptors for read and write activity via CFRunLoop.


CFStringTokenizer allows you to tokenize strings into words, sentences or paragraphs in a language-neutral way. It supports languages such as Japanese and Chinese that do not delimit words by spaces, as well as de-compounding German compounds. You can obtain Latin transcription for tokens. It also provides language identification API.