QHash of QVectors

Question

I have a QHash<QString, QVector<float> > qhash ,and trying to overwite the values in QVector as following:

void Coordinate::normalizeHashElements(QHash<QString, QVector<float> > qhash)
{
    string a = "Cluster";
    float new_value;
    float old_value;
    const char *b = a.c_str();
    float min = getMinHash(qhash);
    float max = getMaxHash(qhash);

    QHashIterator<QString, QVector<float> > i(qhash);
        while (i.hasNext())
        {
            i.next();
            if(i.key().operator !=(b))
            {
                for(int j = 0; j<i.value().size(); j++)
                {
                    old_value = i.value().at(j);
                    new_value = (old_value - min)/(max-min)*(0.99-0.01) + 0.01;
                    i.value().replace(j, new_value);
                }
            }
        }
}

I am getting an error on the i.value().replace(j, new_value); stroke saying following :

C:\Qt\latest test\Prototype\Coordinate.cpp:266: error: passing 'const QVector' as 'this' argument of 'void QVector::replace(int, const T&) [with T = float]' discards qualifiers [-fpermissive]

could anyone help me to fix this?

Answer 1

The error message is telling you that you are attempting to use a non-const method on a const instance. In this case, you are trying to call QVector::replace on a const QVector. The main reason for this is because you are using QHashIterator, which only returns const references from QHashIterator::value().

To fix this, you could use the STL-style iterator instead of the Java-style iterator on the QHash:

QString b("Cluster");
QHash<QString, QVector<float> >::iterator it;
for (it = qhash.begin(); it != qhash.end(); ++it)
{
   if (it.key() != b)
   {
      for (int j=0; i<it.value().size(); j++)
      {
         old_value = it.value().at(j);
         new_value = (old_value-min)/(max-min)*(0.99-0.01) + 0.01;
         it.value().replace(j, new_value);
      }
   }
}

You could also use QMutableHashIterator instead of QHashIterator.