QT Road (2) -- HelloWorld

Hello World

#include <QApplication>
#include <QWidget>
int main(int argc, char *argv[])
{
    
	QApplication a(argc, argv);
	QWidget w;
	w.show();
	return a.exec();
}

• Qt The header file doesn't have .h suffix ;
• Qt A class corresponds to a header file , The class name is the header file name ;
• QApplication Application class ：
  • Manage control flow and main settings for GUI applications .
  • yes Qt The lifeblood of the whole backstage management she includes Main event loop , In which... From window systems and other resources All event handling and scheduling . It also handles Initialization and end of application , also Provide dialog management .
  • For any use Qt The GUI application for , There just happens to be one QApplication object , Whether or not the application has 0、1、2 Or more windows .
• a.exec()
  The program enters the message loop , Waiting for the corresponding user input . here main() Transfer control to Qt,Qt Complete the event handling work , When the application exits exec() Will return . stay exec() in ,Qt Accept and process user and system events and pass them to the appropriate widgets .