[Qt-interest] Problem with qSort and QObjects

[Carl Snellman]

Hey all,

I've been fighting to get qSort working with following code: (adopted
from http://lists.trolltech.com/qt-interest/2008-07/thread00695-0.html)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
#include <QtCore/QCoreApplication>
#include <iostream>
#include <QtAlgorithms>
#include <QDebug>
#include <QObject>

class Account : QObject {
public:
    Account() {};
    Account(QString aItem, QString bItem)
             : aItem(aItem), bItem(bItem) {};
    QString aItem;
    QString bItem;
    QString toString(){
        QString result;
        return result.append("aItem = ").append(aItem).append("\t")
                .append("bItem = ").append(bItem).append("\n");
    };
    bool operator<(const Account & other ) const {
        qDebug() << "Comparing: " << aItem << ":" << other.aItem;
        return aItem < other.aItem;
    };
};

int main(int argc, char *argv[]) {
    QCoreApplication a(argc, argv);
    QList<Account> list;
    list << Account("item 5", "Dummy");
    list << Account("item 1", "Dummy");
    list << Account("item 3", "Dummy");
    list << Account("item 4", "Dummy");
    list << Account("item 2", "Dummy");

    for (int i=0; i<5; ++i)
        std::cout << list.value(i).toString().toStdString();
    std::cout << "==================\n";

    qSort(list);

    for (int i=0; i<5; ++i)
        std::cout << list.value(i).toString().toStdString();
    return 0;
}
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Above gives me the following compilation errors:

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Running build steps for project qSortAccountTest...
Configuration unchanged, skipping QMake step.
Starting: /usr/bin/make -w
make: Entering directory
`/scratchbox/users/maemo/home/maemo/qSortAccountTest/qSortAccountTest'
g++ -c -pipe -g -Wall -W -D_REENTRANT -DQT_CORE_LIB -DQT_SHARED
-I/home/maemo/qtsdk-2010.01/qt/mkspecs/linux-g++ -I.
-I/home/maemo/qtsdk-2010.01/qt/include/QtCore
-I/home/maemo/qtsdk-2010.01/qt/include -I. -o main.o main.cpp
/home/maemo/qtsdk-2010.01/qt/include/QtCore/qobject.h: In copy
constructor 'Account::Account(const Account&)':
main.cpp:7: instantiated from 'T QList<T>::value(int) const [with T = Account]'
main.cpp:35: instantiated from here
/home/maemo/qtsdk-2010.01/qt/include/QtCore/qobject.h:309: error:
'QObject::QObject(const QObject&)' is private
main.cpp:7: error: within this context
/home/maemo/qtsdk-2010.01/qt/include/QtCore/qlist.h: In member
function 'T QList<T>::value(int) const [with T = Account]':
/home/maemo/qtsdk-2010.01/qt/include/QtCore/qlist.h:589: note:
synthesized method 'Account::Account(const Account&)' first required
here
/home/maemo/qtsdk-2010.01/qt/include/QtCore/qobject.h: In member
function 'Account& Account::operator=(const Account&)':
main.cpp:7: instantiated from 'void
QList<T>::node_construct(QList<T>::Node*, const T&) [with T =
Account]'
/home/maemo/qtsdk-2010.01/qt/include/QtCore/qlist.h:472: instantiated
from 'void QList<T>::append(const T&) [with T = Account]'
/home/maemo/qtsdk-2010.01/qt/include/QtCore/qlist.h:315: instantiated
from 'QList<T>& QList<T>::operator<<(const T&) [with T = Account]'
main.cpp:28: instantiated from here
/home/maemo/qtsdk-2010.01/qt/include/QtCore/qobject.h:309: error:
'QObject& QObject::operator=(const QObject&)' is private
main.cpp:7: error: within this context
/home/maemo/qtsdk-2010.01/qt/include/QtCore/qlist.h: In member
function 'void QList<T>::node_construct(QList<T>::Node*, const T&)
[with T = Account]':
/home/maemo/qtsdk-2010.01/qt/include/QtCore/qlist.h:353: note:
synthesized method 'Account& Account::operator=(const Account&)' first
required here
make: Leaving directory
`/scratchbox/users/maemo/home/maemo/qSortAccountTest/qSortAccountTest'
make: *** [main.o] Error 1
Exited with code 2.
Error while building project qSortAccountTest
When executing build step 'Make'
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Now, if I change the Account class not to extend QObject, everything
works fine, and output is sorted.
So I would have two questions:
1) What I need to do to get the QObject version working? qSort docs
say that the items need to implement operator<(), but clearly that is
not enough.

2) Is it possible to overload the operator<() this way (using
pointers) and use it with qSort?
    bool operator<(const Account * other ) const;
My app actually stores pointers to objects (extending QObject) in the
QList that I want to sort, so will it be possible at all?

Any help is greatly appreciated!
Thanks,
Carl