Calling method from member object

Question

I have a problem with calling member method of object which is a member of some class. What I mean? I have class CPosition :

cposition.h

#ifndef CPOSITION_H
#define CPOSITION_H

class CPosition
{
public:
    CPosition(QString name, QString description);
    QString toString();

private:
    QString m_name;
    QString m_description;

};

#endif // CPOSITION_H

cposition.cpp

#include <QString>
#include "cposition.h"

CPosition::CPosition(QString name, QString description)
    : m_name(name), m_description(description)
{

}

QString toString()
{
    QString test("Test - method called!");
    return test;
}

And then I have a class CPerson in which one of member is pointer to CPosition object. In method CPerson::getPosition I would like to call method CPosition::getPosition only if pointer exist:

cperson.h

#ifndef CPERSON_H
#define CPERSON_H

class CPosition;

class CPerson
{
public:
    CPerson(QString name);
    QString getPosition();

private:
    QString m_name;
    CPosition * m_position;
    CEmployer * m_employer;
};

#endif // CPERSON_H

cperson.cpp

#include <QTextStream>
#include <QString>
#include "cperson.h"
#include "cposition.h"

CPerson::CPerson(QString name) : m_name(name){}

QString CPerson::getPosition()
{
    QString str;
    QTextStream cout(&str);
    if(m_position) //here check if pointer exist
    {
        cout << "Position: " << m_position->toString(); //<---- here is problem
    }
    else
        cout << "Position doesn't exist!!!" << endl;
    return str;
}

When I build this project I get an error:

C:\Qt\Projects\Tutorial\qt2\cperson.cpp:28: error: undefined reference to `CPosition::toString()'

I'm using QtCreator IDE. Does anyone can help me with this issue or explain why this isn't working ?

Answer 1

When you define your toString() method with

QString toString()
{
   //code
}

prototype in cposition.cpp file, it's not a member of the CPosition class. That's why when you try to call this method from m_position pointer which is of type CPosition , you get undefined reference error because you haven't implemented the toString() method decalred in cposition.h file.

Change the prototype of the toString() method in cposition.cpp file from

QString toString()

to

QString CPosition::toString()
{
   //write code here
}

so that compiler knows that toString() method implemented in cposition.cpp file is the one declared in cposition.h file.

Answer 2

Basically you are not giving an implementation to the toString method. The correct way should be:

QString CPosition::toString()
{
    QString test("Test - method called!");
    return test;
}