Question about read-only object.

[robgeek]

Good evening!

Why i'm getting the following error message? How can i fix it?

QList<Number> Historic::descendingOrder(QList<Number> ranking)
{
    Number aux(0, 0);
    int length = ranking.size( );
 
    for(int i = 0; i < length; i++)
    {
        for(int j = 0; j < (length - 1); j++)
        {
            if(ranking.at( j ).acum < ranking.at(j + 1).acum)
            {
                aux.val = ranking.at(j + 1).val;
                aux.acum = ranking.at(j + 1).acum;
                ranking.at(j + 1).val = ranking.at( j ).val; //Error message here
                ranking.at(j + 1).acum = ranking.at( j ).acum; //Error message here
                ranking.at( j ).val = aux.val; //Error message here
                ranking.at( j ).acum = aux.acum; //Error message here
            }
        }
    }
 
    return ranking;
}

QList<Number> Historic::descendingOrder(QList<Number> ranking)
{
    Number aux(0, 0);
    int length = ranking.size( );

    for(int i = 0; i < length; i++)
    {
        for(int j = 0; j < (length - 1); j++)
        {
            if(ranking.at( j ).acum < ranking.at(j + 1).acum)
            {
                aux.val = ranking.at(j + 1).val;
                aux.acum = ranking.at(j + 1).acum;
                ranking.at(j + 1).val = ranking.at( j ).val; //Error message here
                ranking.at(j + 1).acum = ranking.at( j ).acum; //Error message here
                ranking.at( j ).val = aux.val; //Error message here
                ranking.at( j ).acum = aux.acum; //Error message here
            }
        }
    }

    return ranking;
}

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D:\Programming\C-C++\Qt\Windows\historic.cpp:121: error: assignment of member 'Number::val' in read-only object
ranking.at(j + 1).val = ranking.at( j ).val;

Everything in "Number" class is public. I don't understand!

[wysota]

at() returns a const object, you cannot assign to it. Use the index operator instead.

[robgeek]

at() returns a const object, you cannot assign to it. Use the index operator instead.

What do you think about using [ ] instead of indexOf() or at() with QList and QVector?

[anda_skoa]

I think what you are really looking for is a generic sorting algorithm, like std::sort() or qSort()

Cheers,
_