type conversion in C++/QT Qstring

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Hi programmers!
I have one issue while i am fetching data from DLL file.

C++

if (PCANReadS == PCAN_ERROR_OK)
{
    Dataid = QString::number(msg.ID, 16);
    nt temp =* (int*)msg.DATA;
    MsgType = msg.MSGTYPE;
    //MsgDLC = msg.LEN;
    MsgDLC = QString::number(msg.LEN, 10);
    Datain = QString::number(temp, 16);
    TStmpMilliCurrent = QString::number(timestamp.millis, 10);
    TStmpMicroCurrent = QString::number(timestamp.micros, 10);
}

What i want to do is getting the difference between current time stamp and previous.
When i subtract it gives me error because both are in Qstring.
How i can get this difference between two time stamps?

Posted 11-Nov-15 3:32am

Ramiien

Updated 11-Nov-15 4:29am

George Jonsson

v3

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Comments

Jochen Arndt 11-Nov-15 9:54am

Why you are converting all numbers to QString?
Just subtract the previous numbers (which are not present in your example) from the current ones.

Ramiien 11-Nov-15 9:58am

int TStmpMilliCurrentInt = atoi(TStmpMilliCurrent);

getting msg cannot convert Qstring to const Char

Jochen Arndt 11-Nov-15 10:06am

Why do you convert a number to a QString and try to convert it back to a number later?

A QString contains Unicode strings (UTF-16). So you must use the wide character functions (e.g. _wtoi with Windows) or the QString member function toInt().

Ramiien 11-Nov-15 10:18am

Actually i am getting time in milli seconds from CAN and trying to get the time difference between two frames

Jochen Arndt 11-Nov-15 10:22am

Then store the time in a variable (as number) and when receiving the next frame calculate the difference and write the new time afterwards into the variable.
[EDIT]
The variable must hold its value. So it must be a global one or a C++ class member when the class is not destroyed.

Ramiien 11-Nov-15 10:28am

this is what i tried e.g
TStmpMilliCurrent= QString::number(timestamp.millis, 10); //getting time
int myprevTime= TStmpMilliCurrent; // trying to put it in other variable

but its not possible i am trying to put string to int. How i can do this?

Jochen Arndt 11-Nov-15 10:40am

I answered that already: Use _wtoi() or QString::toInt().

But see my answer on how to do it. Even your QString must be stored global to save the time stamp.

Richard MacCutchan 11-Nov-15 11:12am

QString::number(timestamp.millis, 10) converts an integer to a string. See http://doc.qt.io/qt-5/qstring.html.

George Jonsson 11-Nov-15 10:31am

Good luck. :-)

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Jochen Arndt · Accepted Answer · 2015-11-11T04:38:00

An incomplete example on how to store a timestamp based on the available code:

C++

int prevTime = 0;

void someFunction()
{
    if (PCANReadS == PCAN_ERROR_OK)
    {
        int diffTime = 0;
        // If not first frame
        if (prevTime)
            difftime = timestamp.millis - prevTime;
        prevTime = timestamp.millis;
    }
}

It would be better to use the same type as timestamp for the global variable. But I did not know the type.