Question

I’m writing a C++ program using Code::Blocks. I want to make a doubly linked list.

My plan is to make an node class called geoPoint with pointers north and south to other nodes. I’ve written a test function to create and link two nodes, then traverse them with a third node. Here’s what I have so far:

#include <iostream>
#include <string>

using namespace std;

class geoPoint
{
    public:
    geoPoint *north, *south;

    private:
    string description;

    public:
    void showDesc()
    {
        cout << description << endl;
    };
    void setDesc(string sourceText)
    {
        description=sourceText;
    };
    void setNorth(geoPoint sourcePoint)
    {
        north= &sourcePoint;
    }
    void setSouth(geoPoint sourcePoint)
    {
        south= &sourcePoint;
    }
};

int main()
{
    geoPoint testPoint,testPoint2,currentPoint;
    string sourceText("testPoint");
    string sourceText2("testPoint2");
    testPoint.setDesc(sourceText);
    testPoint2.setDesc(sourceText2);
    testPoint.setNorth(testPoint2);
    testPoint2.setSouth(testPoint);
    currentPoint=testPoint;
    currentPoint.showDesc();
    currentPoint= &currentPoint.north;
    currentPoint.showDesc();
    cin.get();
    return 0;
};

main() crashes when it gets to the line currentPoint= &currentPoint.north;. The error message is:
error: no match for 'operator=' in 'currentPoint = & currentPoint.geoPoint::north'

I thought that a=&b is the right way to assign the dereferenced contents of pointer b to variable a. What am I doing wrong?

Answer 1

currentPoint is of type geoPoint. &currentPoint.north is of type geoPoint**. & is the address-of operator: you’re taking the address of a geoPoint*, which stores the address of a geoPoint.

If you want currentPoint to hold a copy of the geoPoint to which currentPoint.north refers, use the dereference operator *, as in *currentPoint.north. However, if you merely want to refer to the object without copying it, change currentPoint to a geoPoint* and write this instead:

currentPoint = currentPoint->north;