C++ and const - accessing a member function of a const reference

Question

I have this snippet of code here. The intention is to make a copy of initialData. Since I am not modifying initialData in any way, I figure that I should pass it as a const reference. However, I keep getting this message when compiling.

.\src\Scene\SceneAnimationData.cpp(23) : error C2662: 'SceneTrackerData::getRect' : cannot convert 'this' pointer from 'const SceneTrackerData' to 'SceneTrackerData &'

#include "SceneTrackerData.h"

void SceneAnimationData::SetupData(const SceneTrackerData &initialData)
{
    // getRect(), points() and links() all return const pointers
    CloneRect(initialData.getRect());
    ClonePoints(initialData.points()->values());
    CloneLinks(initialData.links()->values());
}

void SceneAnimationData::CloneRect(const QGraphicsRectItem * initialRect) 
{
    if (initialRect != NULL)
    {
        QPointF position = initialRect->scenePos();
        QRectF rect = initialRect->rect();

        initialRect = new QGraphicsRectItem(rect);
        initialRect->setPos(position);
    }
}

void SceneAnimationData::CloneLinks(const QList<QGraphicsLineItem*> links) 
{
    links_ = new QList<QGraphicsLineItem*>(*links);
}

void SceneAnimationData::ClonePoints(const QList<QGraphicsEllipseItem*> points) 
{
    points_ = new QList<QGraphicsEllipseItem*>(*points);
}

Answer 1

Without the definition of SceneTrackerData, it's hard to say, but likely that function (SceneTrackerData::getRect) is not marked as const.

That is, what is (guessing):

const Rect& SceneTrackerData::getRect(void)

Should be:

const Rect& SceneTrackerData::getRect(void) const 
                        //                     ^
                        //                     |
                        // does not logically modify the object

Answer 2

It's not clear which is line 23 here; but my guess is that you are calling methods on the object that are not themselves declared as const and thus are not usable by a const object reference.