---
title: "BNNSGraphContextSetMessageLogCallback(_:_:_:)"
framework: accelerate
role: symbol
role_heading: Function
path: "accelerate/bnnsgraphcontextsetmessagelogcallback(_:_:_:)"
---

# BNNSGraphContextSetMessageLogCallback(_:_:_:)

Specifies a customized callback function that reports execution-time messages.

## Declaration

```swift
func BNNSGraphContextSetMessageLogCallback(_ context: bnns_graph_context_t, _ log_callback_fn: bnns_graph_execute_message_fn_t, _ additional_logging_arguments: UnsafeMutablePointer<bnns_user_message_data_t>?) -> Int32
```

## Parameters

- `context`: The graph context.
- `log_callback_fn`: The message-logging callback function.
- `additional_logging_arguments`: Additional data for the message logging functions that BNNS passes unaltered to the callback function.

## Return Value

Return Value 0 on success, nonzero on failure.

## Discussion

Discussion The following code adds a custom context execute-message callback function that prints messages to the console: BNNSGraphContextSetMessageLogCallback(context, messageLogCallback, nil)

func messageLogCallback(msg_level: BNNSGraphMessageLevel,                         error_msg: UnsafePointer<CChar>,                         op_info: UnsafePointer<CChar>?,                         additional_logging_arguments: UnsafeMutablePointer<user_message_data_t>?) {

print(NSString(cString: error_msg, encoding: NSUTF8StringEncoding) ?? "")     if let op_info = op_info {         print(NSString(cString: op_info, encoding: NSUTF8StringEncoding) ?? "")     } }

## See Also

### Specifying a context’s execute-time message callback

- [bnns_graph_execute_message_fn_t](accelerate/bnns_graph_execute_message_fn_t.md)
- [BNNSGraphMessageLevel](accelerate/bnnsgraphmessagelevel.md)
- [bnns_user_message_data_t](accelerate/bnns_user_message_data_t.md)