QT C++ prevent Runtime Error when close app - c++

Question

I'm writing a QT application and everything is fine with building and working but when i close the app with a thread running, the app closes and shows a message:
[Runtime Error....].
The application output says:
QThread: Destroyed while thread is still running
The program has unexpectedly finished.
The process was ended forcefully.
example crashed.
how to solve that ?
Example:
main.cpp
#include "mainwindow.h"
#include <QApplication>
#include <QString>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
example = new Thread(this);
connect(example, SIGNAL(print_line(QString)), this, SLOT(print_line2(QString)), Qt::BlockingQueuedConnection);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::print_line2(QString in)
{
ui->textBrowser->append(in);
}
void MainWindow::on_pushButton_clicked()
{
example->start();
}
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <Thread.h>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
Thread *example;
public slots:
void print_line2(QString in);
private slots:
void on_pushButton_clicked();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
Thread.cpp
#include "Thread.h"
#include <windows.h>
using namespace std;
Thread::Thread(QObject *parent):
QThread(parent)
{
}
Thread::~QThread()
{
delete ui;
}
void Thread::print(QString in)
{
print_line(in);
}
void Thread::run()
{
int count = 0;
for(;;) {
Sleep(100);
count += 1;
print(QString::number(count));
}
}
Thread.h
#ifndef READINFO_H
#define READINFO_H
#include <QThread>
class Thread : public QThread
{
Q_OBJECT
public:
explicit Thread(QObject *parent =0);
void print(QString in);
void run();
signals:
void print_line(QString x);
};
#endif
Ready example

Answer 1

The problem is that the thread is still in the running state when your application shuts down.
The code inside Thread::Run() contains an infinite loop -- there is no way for it to terminate by itself. You need to write your thread so that it will exit, or at the very least, you need to forcefully terminate the thread before your app closes.
To forcefully terminate, you could add two lines of code to the MainWindow destructor like so:
MainWindow::~MainWindow()
{
example->terminate();
example->wait();
(...)
}