Basic knowledge of QT original code

 untitled1.pro

#-------------------------------------------------
#
# Project created by QtCreator 2022-06-28T09:57:30
#
#-------------------------------------------------
# Qt Modules applied to 
QT       += core gui
#  Compatible with previous Qt edition （ It doesn't usually change ）
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
#  The name of the generated application 
TARGET = untitled1
#  Refers to generated makfile type 
TEMPLATE = app

# The following define makes your compiler emit warnings if you use
# any feature of Qt which has been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

#  Source file 
SOURCES += \
        main.cpp \
        widget.cpp
#  The header file 
HEADERS += \
        widget.h
# UI file 
FORMS += \
        widget.ui

# Qt Modules applied to 

QT       += core gui

#  Compatible with previous Qt edition （ It doesn't usually change ）

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

#  The name of the generated application 

TARGET = untitled1

#  Refers to generated makfile type 

TEMPLATE = app

widget.h in  

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
// Definition UI The namespace of 
namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT    // macro   If signals and slots are used , This class must be added 

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();

private:
    Ui::Widget *ui; // use UI In the namespace Widget class , Define a pointer *ui
};

#endif // WIDGET_H

Q_OBJECT // macro If signals and slots are used , This class must be added

Ui::Widget *ui; // use UI In the namespace Widget class , Define a pointer *ui

 widget.cpp in

#include "widget.h"
#include "ui_widget.h"

// Constructors 
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
}

Widget::~Widget()
{
    delete ui;
}

 main.cpp

#include "widget.h"     // Because the main function uses a window , Need to import header file 
#include <QApplication>

int main(int argc, char *argv[])
{
    // Application class , Every Qt There is only one application object in the application 
    QApplication a(argc, argv);
    // Window classes create window objects , When the window is created, it will not be displayed by default 
    Widget w;   // top window 
    w.show();   // Window display 

    return a.exec();    // The application object runs 
}

exec() What is the function of ？

The function is to start a cycle , Execute an event , amount to while(1) and for(;;). Make sure the window doesn't flash