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QList Help

  • Hi everyone,
    here's my issue, i'm trying to get QList data from a class to my main.
    My code is suppose to get a joystick event then i put it in a QList which i then return,see the code below.
    here is my code :

    QList <int> Rjoystick::datAxis(int i)
        QList <int>axis;
        m_joystick = SDL_JoystickOpen(i);
        SDL_Event event;
        switch (event.type) {
        return axis;

    and here's the code fto get some data from the QList on the main.

    QList <int> g;
       g = r.datAxis(0);
       qDebug() <<;

    i'm getting this error : "ASSERT failure in QList<T>::at: "index out of range"

    thamk you foryour help.

  • Lifetime Qt Champion


    There's no garanti that datAxis returns a non empty list. You should check that before using that function return value.

  • So i modify the code and it's seems that you are right, i think my problem maybe coming from the function "insert". At this point i don't know how will i get the Joystick data into my QList, if you got any advice, i will take it.

  • Lifetime Qt Champion

    I was wondering something else
    what is
    What values do they have?
    As if event.jaxis.axis is not zero, you ask it to insert event.jaxis.value at some
    index which list might not have (yet) -> giving "index out of range"
    You could do
    axis.append(event.jaxis.value); to simply store the values but
    you might need event.jaxis.axis for something also ?

  • Well, event.jaxis.axis hold a integer it's the axis being moved, can be 0 or 4 depends of what axis of the joystick is being moved.
    And event.jaxis.value hold the value of the which the joystick is moved can be anything between roughly -32000 to 32000.

  • Lifetime Qt Champion

    In that case, you could do
    QList<int> axis{0,0,0,0,0};
    will work as expected.
    (as list has 5 ints)
    I assume then event.jaxis.axis can have value 0-4 ?
    When you read it back you can check which index has non zero to see
    which axes was changed.

  • Did that, And it is working just perfectly.

    Thank you for help.

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