MessageHandlerExample.cpp

static const QtMessageHandler QT_DEFAULT_MESSAGE_HANDLER = qInstallMessageHandler(0);

void messageHandler(QtMsgType type, const QMessageLogContext& context, const QString& msg)
{
  QString categoryString = QString(context.category);

  if (categoryString.compare("default") == 0 || categoryString.compare("qml") == 0) {
    switch (type) {
      case QtDebugMsg:
        qCDebug(category) << msg;
        break;

      case QtWarningMsg:
        qCWarning(category) << msg;
        break;
        
      case QtCriticalMsg:
        qCCritical(category) << msg;
        break;
        
      case QtFatalMsg:
        qCFatal(category) << msg;
        break;   
      }
  }
  else {
    (*QT_DEFAULT_MESSAGE_HANDLER)(type, context, msg + categoryString);
    
    if (type == QtFatalMsg) {
      abort();
    }
  }
}

int main(int argc, char* argv[])
{
  qInstallMessageHandler(messageHandler);
...