QTime stops and do not want to continue

? Offline

Hello,

in a part of my program I want to find out a time difference between the last call and now but my temporary variable stops working:

@...
QTime current_time= QTime::currentTime();
QTime time_temp;
quint16 time_delta;

current_time = QTime::currentTime();

while(1){

    time_temp = current_time; //save time
    current_time = QTime::currentTime(); //current time
    absolute_frames++;
    time_delta = (current_time.second()*1000 + current_time.msec()) - (time_temp.second()*1000 + time_temp.msec());

    if(time_delta > 1000)
    {
        current_time = time_temp;
        qDebug() << "time problem!";
    }
    qDebug() << "time_temp:" << time_temp << " current_time:" << current_time << " time_delta:" << time_delta;

}
...@
At some point, I get the qDebug() message and the value of time temp never changed from this moment although I wrote:
@time_temp = current_time; //save time@

Does anybody know what it could be or what my mistake is?

? Offline

Oh i found out both "time_temp" and "current_time" does not change their values any more.

ckakman

Is this your actual code or have you just made up an example to post here?

? Offline

This is just an extract

ckakman

So it is production code then, but I don't see any breaks in that loop. And you are not doing anything in the loop except qDebug()s.

I don't think this is the actual code. I can't go on with what you have provided.

? Offline

My original file includes more than 500 lines of code.

Now i wrote a complete new one. This is it:

@#include <QCoreApplication>
#include <QTime>
#include <QDebug>

int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);

QTime current_time= QTime::currentTime();
QTime time_temp;
quint16 time_delta;

current_time = QTime::currentTime();

while(1)
{
    time_temp = current_time; //save time
    current_time = QTime::currentTime(); //current time

    time_delta = (current_time.second()*1000 + current_time.msec()) - (time_temp.second()*1000 + time_temp.msec());

    if(time_delta > 1000)
    {
        current_time = time_temp;
        qDebug() << "time problem!";
    }
    qDebug() << "time_temp:" << time_temp << " current_time:" << current_time << " time_delta:" << time_delta;
}

return a.exec&#40;&#41;;

}@

The same problem after some seconds. Both variables do not change their values after seconds.

ckakman

You are assigning time_temp back to current_time if time_delta gets larger than 1000. Then you assign current_time back to time_temp at beginning of the loop. You never update time_temp with current_time thereafter.

Remove line 24 in the if block:
@
current_time = time_temp;
@

? Offline

Yes I could but i need the approximate time difference. My problem is that at one point the values of the variable "current_time" never change. If I print the values of "current_time" the values or the variables are frozen but QTime::currentTime is running. I can not change the values of "current_time" with the command any more:
@current_time = QTime::currentTime();@

JKSH

Hi,

-Your loop is running at max speed (it makes your CPU run at 100%), and it is flooding your system with thousands of debug messages. I'm guessing that your program has actually frozen.-

-Try adding a delay in your loop and see what happens.-

Also, to measure time deltas, the recommended class is "QElapsedTimer":http://doc.qt.io/qt-5/qelapsedtimer.html

ckakman

[quote author="Bartholomew" date="1421541823"]Yes I could but i need the approximate time difference. My problem is that at one point the values of the variable "current_time" never change. If I print the values of "current_time" the values or the variables are frozen but QTime::currentTime is running. I can not change the values of "current_time" with the command any more:
@current_time = QTime::currentTime();@[/quote]

They are "frozen" because of a logic error in your code as I explained above. Once the difference is larger than 1000, you freeze time_temp by storing it in current_temp. t the next iteration of the loop, you save current_time back to temp_time. Then you update current_time, calculate the difference, which is again larger than 1000 and you again enter the if block. You again update current_time with time_temp. As you see, you never ever update time_temp with the newer value of current_time but instead update current_time with time_temp. This is your logic error, that's why you need to remove line 24.

If you can't follow the explanation above, I suggest you get a pen and track the values of these 2 variables on paper when the delta becomes greater than 1000.

JKSH

[quote author="ckakman" date="1421545003"]They are "frozen" because of a logic error in your code as I explained above.[/quote]Good catch! I need to read more carefully before answering :P