Save QList<int> to QSettings - qt

Question

I want to save a QList<int> to my QSettings without looping through it.
I know that I could use writeArray() and a loop to save all items or to write the QList to a QByteArray and save this but then it is not human readable in my INI file..
Currently I am using the following to transform my QList<int> to QList<QVariant>:
QList<QVariant> variantList;
//Temp is the QList<int>
for (int i = 0; i < temp.size(); i++)
variantList.append(temp.at(i));
And to save this QList<Variant> to my Settings I use the following code:
QVariant list;
list.setValue(variantList);
//saveSession is my QSettings object
saveSession.setValue("MyList", list);
The QList is correctly saved to my INI file as I can see (comma seperated list of my ints)
But the function crashes on exit.
I already tried to use a pointer to my QSettings object instead but then it crashes on deleting the pointer ..

Answer 1

QSettings::setValue() needs QVariant as a second parameter. To pass QList as QVariant, you have to declare it as a Qt meta type. Here's the code snippet that demonstrates how to register a type as meta type:
#include <QCoreApplication>
#include <QDebug>
#include <QMetaType>
#include <QSettings>
#include <QVariant>
Q_DECLARE_METATYPE(QList<int>)
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
qRegisterMetaTypeStreamOperators<QList<int> >("QList<int>");
QList<int> myList;
myList.append(1);
myList.append(2);
myList.append(3);
QSettings settings("Moose Soft", "Facturo-Pro");
settings.setValue("foo", QVariant::fromValue(myList));
QList<int> myList2 = settings.value("foo").value<QList<int> >();
qDebug() << myList2;
return 0;
}

Answer 2

You might have to register QList as a meta-type of its own for it to work. This is a good starting point to read up on meta-types in Qt: http://qt.nokia.com/doc/4.6/qmetatype.html#details .

Answer 3

I was also struggling with this ... and I believe I now have a decent solution.
I hope this saves someone the trouble, it caused me.
#include <QCoreApplication>
#include <QSettings>
#include <QList>
#include <QDataStream>
#include <QVariant>
#include <QVariantList>
#include <QDebug>
#include <deque>
template <class T> static QVariant toVariant(const QList<T> &list)
{
QVariantList variantList;
variantList.reserve(list.size());
for (const auto& v : list)
{
variantList.append(v);
}
return variantList;
}
template <class T> static QList<T> toList(const QVariant &qv)
{
QList <T> dataList;
foreach(QVariant v, qv.value<QVariantList>()) {
dataList << v.value<T>();
}
return dataList;
}
void Gen()
{
QList<QString> data {"hello", "world","how", "are", "you"};
QList<int> ages {10,20,30,40};
QSettings setup("stuff.ini", QSettings::IniFormat);
setup.beginWriteArray("rules");
for (int groups=0;groups<3;groups++)
{
setup.setArrayIndex(groups);
setup.setValue("rule",QString("Rule-%1").arg(groups));
setup.setValue("data", toVariant (data));
setup.setValue("ages", toVariant (ages));
}
setup.endArray();
setup.sync();
}
void Read()
{
QSettings setupR("stuff.ini", QSettings::IniFormat);
int rule_count = setupR.beginReadArray("rules");
for (int groups=0;groups<rule_count;groups++)
{
setupR.setArrayIndex(groups);
QString nameRead = setupR.value("rule").toString();
QList<QString> dataRead = toList<QString>(setupR.value("data"));
qDebug() << "Rule " << groups;
qDebug() << "Rule Read" << nameRead;
qDebug() << "Data Read2" << dataRead;
}
}
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
// Write
Gen();
// Read
Read();
exit(0);
//return a.exec();
}
You should end up with an INI file which looks like this ...
[rules]
1\ages=10, 20, 30, 40
1\data=hello, world, how, are, you
1\rule=Rule-0
2\ages=10, 20, 30, 40
2\data=hello, world, how, are, you
2\rule=Rule-1
3\ages=10, 20, 30, 40
3\data=hello, world, how, are, you
3\rule=Rule-2
size=3
The nice thing here is you can edit this outside of QT (Just be careful) ...