add data to QJsonArray in a loop with C++ Qt - c++

Question

I'm not sure what the correct way to create nested JSON from a loop is in Qt. Here's an example of what I mean
#include <QDebug>
#include <QJsonArray>
#include <QJsonDocument>
#include <QSet>
#include <QString>
#include <QVector>
int main(int argc, char *argv[]) {
QVector<QSet<int>> sets;
QSet<int> testSet;
QJsonDocument doc;
QJsonArray root;
doc.setArray(root);
testSet.insert(0);
testSet.insert(1);
testSet.insert(2);
QSet<int> testSet1;
testSet1.insert(3);
testSet1.insert(4);
sets.push_back(testSet);
sets.push_back(testSet1);
for (auto set : sets) {
QJsonArray setJSON;
for (int i : set) {
setJSON.append(i);
}
root.append(setJSON);
}
qDebug(doc.toJson()); // [ ] -- empty?
}
In the code above, I have a list of sets of integers. I want to represent it as a nested array in JSON. This doesn't work though, because the QJson methods are all pass by reference, meaning that when the scope of the code changes, for instance leaving one of the for loops, the data is destroyed. Is the only way then to do this to create the nested objects on the heap using new? That seems strange to me.

Answer 1

Until now, Qt JSON works only with instance copy, as you see that QJson object is passed as const reference (&) in every set function.
The first QJsonDocument::setArray() take a copy of root instance as its main object. Change of root content after does not affect doc content.
You can verify the root content after the for block :
qDebug() << QJsonDocument( root ).toJson();
The doc variable should be assigned at where you want to take the actual root content:
doc = QJsonDocument (root);
Or:
doc.setArray(root)