---
title: AudioFile_WriteProc
framework: audiotoolbox
role: symbol
role_heading: Type Alias
path: audiotoolbox/audiofile_writeproc
---

# AudioFile_WriteProc

A callback for writing file data when used in conjunction with the AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:) or AudioFileCreateWithURL(_:_:_:_:_:) functions.

## Declaration

```swift
typealias AudioFile_WriteProc = (UnsafeMutableRawPointer, Int64, UInt32, UnsafeRawPointer, 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(_:_:_:_:_:_:_:) ordoc://com.apple.audiotoolbox/documentation/AudioToolbox/AudioFileInitializeWithCallbacks(_:_:_:_:_:_:_:_:_:).
- `inPosition`: An offset into the data from which to read.
- `requestCount`: The number of bytes to write.
- `buffer`: A pointer to the buffer containing the data to write.
- `actualCount`: Upon completion, the callback should set this to a pointer to the number of bytes successfully written.

## Return Value

Return Value A result code. See Result Codes.

## Discussion

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

## See Also

### Callbacks

- [AudioFile_ReadProc](audiotoolbox/audiofile_readproc.md)
- [AudioFile_GetSizeProc](audiotoolbox/audiofile_getsizeproc.md)
- [AudioFile_SetSizeProc](audiotoolbox/audiofile_setsizeproc.md)