appending pointers to class to a QList QList<Class* >

Question

In my mainwindow.h I have a QList m_qlServoList which should store pointers to Servo objects:

QList<Servo* > m_qlServoList;

When I try to append a new Servo pointer to the QList:

m_qlServoList.append(new Servo(iID, iBaudRate));

The following Error results:

passing 'const QList<Servo*>' as 'this' argument of 'void QList<T>::append(const T&) [with T = Servo*]' discards qualifiers [-fpermissive]

The Servo class header looks as follows:

class Servo
{
public:
    Servo(const int &iID, const int &iBaudRate);
    ~Servo();

    void write_data(Data const& data) const;
    Data& receive_data() const;

private:
    Data m_oData;
};

It would be great if someone can explain me what I am doing wrong here. And how to correctly append pointers to Servo objects.

Answer 1

While we lack informations, it's likely that your QList<Servo *> is const.

This could happen if your call was made from a const method of the class holding the QList.

Lets see an example:

class MyClass
    {
        private:
          QList<Servo *> m_qlServoList;
        public:
          void addServo(Servo *ptr) const /* Notice the const here */
            {
              m_qlServoList.append(prt); 
            }
     };

/* from main */
MyClass c;
c.addServo(new Servo(iID, iBaudRate));

This code wouldn't compile, because the addServo() method is const, which means that m_qlServoList will be considered as a const QList<Servo *>.