QTimer Usage in C++ Unix / Windows

[rcanerA]

Hello everyone,

This is a basic issue, but i didnt understand why I am failed timer slots. I used Qt 5.7 in console application timer isn't fired timeout signal.

#include <QCoreApplication>
#include "mytimer.h"
#include <QThread>
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
 
    MyTimer* myTimer = new MyTimer();
 
    while(true)
    {
        QThread::yieldCurrentThread();
    }
 
    return a.exec();
}
 
 
#ifndef MYTIMER_H
#define MYTIMER_H
 
#include <QObject>
#include <QTimer>
class MyTimer : public QObject
{
    Q_OBJECT
public:
    explicit MyTimer(QObject *parent = 0);
    QTimer* timerObj;
signals:
 
public slots:
    void TimerTick();
};
 
#endif // MYTIMER_H
 
#include "mytimer.h"
#include "iostream"
MyTimer::MyTimer(QObject *parent) : QObject(parent)
{
    timerObj = new QTimer(this);
    timerObj->setInterval(1000);
    connect(timerObj,SIGNAL(timeout()),this,SLOT(TimerTick()));
    timerObj->start();
}
 
void MyTimer::TimerTick()
{
    std::cout << "Timer Interrupt" << std::endl;
}

#include <QCoreApplication>
#include "mytimer.h"
#include <QThread>
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    MyTimer* myTimer = new MyTimer();

    while(true)
    {
        QThread::yieldCurrentThread();
    }

    return a.exec();
}


#ifndef MYTIMER_H
#define MYTIMER_H

#include <QObject>
#include <QTimer>
class MyTimer : public QObject
{
    Q_OBJECT
public:
    explicit MyTimer(QObject *parent = 0);
    QTimer* timerObj;
signals:

public slots:
    void TimerTick();
};

#endif // MYTIMER_H

#include "mytimer.h"
#include "iostream"
MyTimer::MyTimer(QObject *parent) : QObject(parent)
{
    timerObj = new QTimer(this);
    timerObj->setInterval(1000);
    connect(timerObj,SIGNAL(timeout()),this,SLOT(TimerTick()));
    timerObj->start();
}

void MyTimer::TimerTick()
{
    std::cout << "Timer Interrupt" << std::endl;
}

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[d_stranz]

Your timer does not start running until you call QApplication::exec() (line 15 in your main.cpp) because timers need an event loop and the event loop isn't started until exec() is called. Your infinite while() loop prevents this from ever happening.

[rcanerA]

Thanks it is working now however i dont understand totally. a.exec() is used for what ?

This exec() is like as a thread run function. Am I right?

And also when I dont use QCoreApplication, can timer work anyway?
I mean QCoreApplication a(argc,argv) and a.exec() removed from the main. Rest of the code will be same.

[d_stranz]

And also when I dont use QCoreApplication, can timer work anyway?

No. QApplication is what runs the event loop, and everything in Qt depends on an active event loop. You cannot have a Qt app without a QApplication class and exec().

[rcanerA]

Thnak you so much.