---
title: AudioFile_ReadProc
framework: audiotoolbox
role: symbol
role_heading: Type Alias
path: audiotoolbox/audiofile_readproc
---

# AudioFile_ReadProc

Reads audio data when used in conjunction with the AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:) or AudioFileInitializeWithCallbacks(_:_:_:_:_:_:_:_:_:) functions.)

## Declaration

```swift
typealias AudioFile_ReadProc = (UnsafeMutableRawPointer, Int64, UInt32, UnsafeMutableRawPointer, UnsafeMutablePointer<UInt32>) -> OSStatus
```

## Parameters

- `inClientData`: A pointer to the client data as set in the inClientData parameter to doc://com.apple.audiotoolbox/documentation/AudioToolbox/AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:) or doc://com.apple.audiotoolbox/documentation/AudioToolbox/AudioFileInitializeWithCallbacks(_:_:_:_:_:_:_:_:_:).
- `inPosition`: An offset into the data from which to read.
- `requestCount`: The number of bytes to read.
- `buffer`: A pointer to the buffer in which to put the data read.
- `actualCount`: On output, the callback should set this parameter to a pointer to the number of bytes successfully read.

## Return Value

Return Value A result code. See Result Codes.

## Discussion

Discussion If you named your function MyAudioFile_ReadProc, you would declare it like this: Discussion This callback function is called when Audio File Services needs to read data.

## See Also

### Callbacks

- [AudioFile_WriteProc](audiotoolbox/audiofile_writeproc.md)
- [AudioFile_GetSizeProc](audiotoolbox/audiofile_getsizeproc.md)
- [AudioFile_SetSizeProc](audiotoolbox/audiofile_setsizeproc.md)