---
title: dispatch_io_handler_t
framework: dispatch
role: symbol
role_heading: Type Alias
path: dispatch/dispatch_io_handler_t
---

# dispatch_io_handler_t

A handler block used to process operations on a dispatch I/O channel.

## Declaration

```occ
typedef void (^)(_Bool, NSObject<OS_dispatch_data> *, int) dispatch_io_handler_t;
```

## Discussion

Discussion The parameters of a dispatch I/O handler are as follows: done - A flag indicating whether the operation is complete. data - The data object to be handled. This object is retained by the system for the duration of the handler’s execution and is released when the handler block returns. error - The error number (if any) reported for the operation. An error number of 0 typically indicates the operation was successful.

## See Also

### Reading from the File

- [dispatch_read](dispatch/dispatch_read.md)
- [dispatch_io_read](dispatch/dispatch_io_read.md)