How to overload operator<< for qDebug

Question

I'm trying to create more useful debug messages for my class where store data. My code is looking something like this

#include <QAbstractTableModel>
#include <QDebug>

/**
  * Model for storing data. 
  */
class DataModel : public QAbstractTableModel {
    // for debugging purposes
    friend QDebug operator<< (QDebug d, const DataModel &model);

    //other stuff
};

/**
  * Overloading operator for debugging purposes
  */
QDebug operator<< (QDebug d, const DataModel &model) {
    d << "Hello world!";
    return d;
}

I expect qDebug() << model will print "Hello world!". However, there is alway something like "QAbstractTableModel(0x1c7e520)" on the output.

Do you have any idea what's wrong?

Answer 1

I know it long time now, but just to be documented and to help any other people who eventually come here having the same doubt, the easiest way to get qDebug() << working with your own class printing something like "Hello World" or whatever else, is to implement implicit conversion of your class to a printable type, like QString (which is well supported by QDebug).

class Foo {
public:
   Foo() { }
   operator QString() const { return <put your QString here>; }   

};