---
title: "CFReadStreamRead(_:_:_:)"
framework: corefoundation
role: symbol
role_heading: Function
path: "corefoundation/cfreadstreamread(_:_:_:)"
---

# CFReadStreamRead(_:_:_:)

Reads data from a readable stream.

## Declaration

```swift
func CFReadStreamRead(_ stream: CFReadStream!, _ buffer: UnsafeMutablePointer<UInt8>!, _ bufferLength: CFIndex) -> CFIndex
```

## Parameters

- `stream`: The stream from which to read.
- `buffer`: The buffer into which to place the data.
- `bufferLength`: The size of buffer and the maximum number of bytes to read.

## Return Value

Return Value The number of bytes read; 0 if the stream has reached its end; or -1 if either the stream is not open or an error occurs.

## Discussion

Discussion If stream is in the process of opening, this function waits until it has completed. This function blocks until at least one byte is available; it does not block until buffer is filled. To avoid blocking, call this function only if CFReadStreamHasBytesAvailable(_:) returns TRUE or after the stream’s client (set with CFReadStreamSetClient(_:_:_:_:)) is notified of a hasBytesAvailable event.