# BNNSGraphCompileOptionsSetMessageLogCallback(_:_:_:) Specifies a customized callback function that reports compile-time messages. ``` func BNNSGraphCompileOptionsSetMessageLogCallback(_ options: bnns_graph_compile_options_t, _ log_callback: bnns_graph_compile_message_fn_t, _ additional_logging_arguments: UnsafeMutablePointer?) ``` ## Parameters `options` The compilation options object. `log_callback` The message-logging callback function. `additional_logging_arguments` Additional data for the message-logging functions that BNNS passes unaltered to the callback function. ## Discussion If you don’t specify this callback, default callback functions log messages to . The following code adds a custom graph compile message callback function that prints [`BNNSGraphMessageLevelInfo`](/documentation/Accelerate/BNNSGraphMessageLevelInfo) level messages to the console: ```swift let options = BNNSGraphCompileOptionsMakeDefault() defer { BNNSGraphCompileOptionsDestroy(options) } BNNSGraphCompileOptionsSetMessageLogMask(options, BNNSGraphMessageLevelInfo.rawValue) BNNSGraphCompileOptionsSetMessageLogCallback(options, messageLogCallback, nil) func messageLogCallback(msg_level: BNNSGraphMessageLevel, error_msg: UnsafePointer, source_location: UnsafePointer?, user_message_data_t:UnsafeMutablePointer?) { print(NSString(cString: error_msg, encoding: NSUTF8StringEncoding) ?? "") if let source_location = source_location { print(NSString(cString: source_location, encoding: NSUTF8StringEncoding) ?? "") } } ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)