Help creating a tree that traverses the map of a graph

Trayon

Reinstalled QT. Thanks for that tip. It got rid of those errors, but now I'm getting something a bit odd.

The error I got was:
no matching function for call to ‘QVector<TreeMap>::indexOf(const TreeMap)’*

Here:

int TreeMap::nodeIndex() const
{
    if (parent)
        return parent->nodes.indexOf(this);

    return 0;
}

Here's TreeMap.h for reference:

#ifndef TREEMAP_H
#define TREEMAP_H
#include <QString>
#include <QVector>

class TreeMap
{
public:
    TreeMap(QString name, TreeMap *parentNode = 0);
    ~TreeMap();

    TreeMap nodeAt(int position) const;
    int nodeCount() const;
    QString data() const;
    bool insertNode(int position);
    TreeMap* getParent();
    bool removeNode(int position);
    int nodeIndex() const;
    bool setData(const QString &value);

private:
    QString nodeName;
    QVector<TreeMap> nodes;
    TreeMap *parent;
};

#endif // TREEMAP_H

SGaist

Hi,

You have a QVector of TreeMap object, this is a pointer to the current object.

mrjj

Hi

nodes.indexOf(this);

"This" is a const TreeMap *
but it wants a &
int indexOf(const T &t, int from = 0) const;

so you can do

int TreeMap::nodeIndex() const {
nodes.indexOf(*this);
}

However, QVector wants an assignable data type so you will need some extra functions
http://doc.qt.io/qt-5/containers.html#assignable-data-type

something like (stripped down)

class TreeMap {
public:
  TreeMap(QString name, TreeMap* parentNode = 0) {}
  int nodeIndex() const;
  TreeMap(const TreeMap& other) {/* IMPLEMENT*/}
  TreeMap& operator=(const TreeMap& other) {/* IMPLEMENT*/}
  bool operator==(const TreeMap& other) {/* IMPLEMENT*/} // most likely wants this too
private:
  QVector<TreeMap> nodes;
};

Trayon

Thanks mrjj.

A few more things to add. You most likely know I'm following the example here:
http://doc.qt.io/qt-5/qtwidgets-itemviews-editabletreemodel-example.html

Why is it that the example doesn't implement these functions? QList has the same shortcoming as QVector when I tried changing it. Also, should I start a new thread with the new errors that pop up in my program, or should I continue posting here as they come?

SGaist

That example is using a QList of pointer to TreeItem you are using a QVector of TreeMap object.

mrjj

@Trayon
Hi
The main difference with the sample is that it uses pointers.
QList<TreeItem*>
So it can just compare pointers. ( they are assignable-data-type by nature)

You are use a class directly so it need you to tell it how to compare etc.
since it cannot know what members inside that should be used.

like if we have
class Car {
QString Model;
}

if we have
Car *A = new Car;
and
Car *B = new Car;
we can say if ( A == B ) and it compiler can just check is the memory address is the same.
But if we do
Car A;
Car B;
and say if ( A == B )
then what should it compare.
we can then "explain it" to the compiler with
if ( A.model == B.model )
and that is what we do with
operator==(..)

@SGaist (hehe ninjaed)

Trayon

Yes, but as I said, I tried changing it to QList, and it had the same shortcomings. Down the error line, I even saw the "no match for '=='" error for QList as well.

mrjj

@Trayon
Yes, as explained it dont know how to compare your class when its NOT pointers.

Trayon

Okay, that explains a lot. Thank you guys for all the help. When I get errors in this project down the line, should I revive this thread, or start a new one?

mrjj

@Trayon
Best with new post with good title so its not mega posts :)

mrjj

Just as a last note:
You can also use
std::vector<TreeMap> nodes;
Which can "just work" with your TreeMap since its members
QString nodeName;
TreeMap *parent;

Is just copyable but mind the parent pointer as it will just copy it as raw pointer and
it might not be what you want/need.