---
title: "CFReadStreamOpen(_:)"
framework: corefoundation
role: symbol
role_heading: Function
path: "corefoundation/cfreadstreamopen(_:)"
---

# CFReadStreamOpen(_:)

Opens a stream for reading.

## Declaration

```swift
func CFReadStreamOpen(_ stream: CFReadStream!) -> Bool
```

## Parameters

- `stream`: The stream to open.

## Return Value

Return Value TRUE if stream was successfully opened, FALSE otherwise. If stream is not in the CFStreamStatus.notOpen state, this function returns FALSE.

## Discussion

Discussion Opening a stream causes it to reserve all the system resources it requires. If the stream can open in the background without blocking, this function always returns true. To learn when a background open operation completes, you can either schedule the stream into a run loop with CFReadStreamScheduleWithRunLoop(_:_:_:) and wait for the stream’s client (set with CFReadStreamSetClient(_:_:_:_:)) to be notified or you can poll the stream using CFReadStreamGetStatus(_:), waiting for a status of CFStreamStatus.open or CFStreamStatus.error. You do not need to wait until a stream has finished opening in the background before calling the CFReadStreamRead(_:_:_:) function. The read operation will simply block until the open has completed.

## See Also

### Opening and Closing a Read Stream

- [CFReadStreamClose(_:)](corefoundation/cfreadstreamclose(_:).md)