2. QT components used in the project

Preface

• Before starting the development project , We need to be aware of the QT Component to introduce some usage

---

One 、QString and QDebug

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QString>
#include <QDebug>

int main(int argc, char *argv[])
{
    
	//QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

	//QGuiApplication app(argc, argv);

	//QQmlApplicationEngine engine;
	//engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
	//if (engine.rootObjects().isEmpty())
	// return -1;

	//return app.exec();

	QString str = "C:/";
	QString str2 = "D:\\";
	qDebug() << str << endl;
	qDebug() << str2 << endl;

	// Splicing 
	str += "muying/";
	str2.append("muying/");
	qDebug() << str << endl;
	qDebug() << str2 << endl;

	// Empty 
	str.clear();

	// String search 
	int pos = str2.indexOf("\\");
	pos = str.indexOf("X");

	//QStringLiteral yes QString The macro , Use this macro to calculate the length of the string 
	// Intercepting string ,param1= Intercept start position ,param2= Intercept length 
	str2 = str2.mid(pos + 1, QStringLiteral("muying").length());
	qDebug() << str << endl;
	qDebug() << str2 << endl;

	// Numbers  ->  character string ： Transformation method 1
	str = QString::number(3.14);

	// Numbers  ->  character string ： Transformation method 2
	str.setNum(34);

	// character string  ->  Numbers 
	QString str3 = "123";
	int i = str3.toInt();
	qDebug("The value of str is: %s", qPrintable(str3));//qPrintable macro , Convert to const char*
	qDebug("The value of i is: %d", i);

	str3 = "abc";
	i = str3.toInt(); // Although it cannot be converted , But there is no error ,i=0
	qDebug("The value of str is: %s", qPrintable(str3));
	qDebug("The value of i is: %d", i);


	return 0;
}

---

Two 、QScopedPointer Intelligent pointer

• A simple test ： Adding method blocks is to create method blocks , Release from stack

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QString>
#include <QDebug>

class SPA
{
    
public:
	SPA()
	{
    
		qDebug() << "SPA::SPA()" << endl;
	}
	~SPA()
	{
    
		qDebug() << "SPA::~SPA()" << endl;
	}
};

int main(int argc, char *argv[])
{
    
	// QScopedPointer
	{
    
		QScopedPointer<int> i(new int(3));
		QScopedPointer<SPA> spA(new SPA);
	}
	return 0;
}

• reset Use

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QString>
#include <QDebug>

class SPA
{
    
public:
	SPA()
	{
    
		qDebug() << "SPA::SPA()" << endl;
	}
	~SPA()
	{
    
		qDebug() << "SPA::~SPA()" << endl;
	}
	void Print()
	{
    
		qDebug() << "SPA::Print()" << endl;
	}
};

int main(int argc, char *argv[])
{
    
	// QScopedPointer
	{
    
		QScopedPointer<int> i2(new int(3));
		qDebug("The value of i2 is: %d", *i2);//3
		i2.reset(new int(4));
		qDebug("The value of i2 is: %d", *i2);//4

		QScopedPointer<SPA> spA(new SPA);
		spA->Print();
		QScopedArrayPointer<SPA> spArr(new SPA[10]);// Array version 
	}

	return 0;
}

---

3、 ... and 、QThread Multithreading

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QString>
#include <QDebug>
#include <QThread>

class MyThread :public QThread
{
    
public:
	MyThread()
	{
    
		isStop = false;
	}
	void CloseThread()
	{
    
		isStop = true;
	}
	void run()
	{
    
		while (true)
		{
    
			if (isStop) {
     return; }
			//tr Internationalize and standardize strings 
			qDebug() << tr("MyThread id is: ") << QThread::currentThreadId();
			sleep(1);
		}
	}
private:
	bool isStop;
};

int main(int argc, char *argv[])
{
    
	//  Implement multithreading 
	MyThread thread;
	thread.start();
	while (true)
	{
    
		;
	}
	thread.CloseThread();

	return 0;
}