//This is in .h
class MainWindow : public QMainWindow
explicit MainWindow(QWidget *parent = 0);
void S7API CliCompletion(void *usrPtr, int opCode, int opResult);
//When I say right click and "add definition in mainwindow" I have got this in .cpp
void MainWindow::CliCompletion(void *usrPtr, int opCode, int opResult)
// Now, My problem what is S7API here,I have not encountered like this in C language.What does it do here.what is it.Where do I have to look in Dietel book.