From X-Plane SDK
typedef void (* XPLMError_f)( const char * inMessage);An XPLM error callback is a function that you provide to receive debugging information from the plugin SDK. See XPLMSetErrorCallback for more information. NOTE: for the sake of debugging, your error callback will be called even if your plugin is not enabled, allowing you to receive debug info in your XPluginStart and XPluginStop callbacks. To avoid causing logic errors in the management code, do not call any other plugin routines from your error callback - it is only meant for logging!