How to load QJsonDocument from a file - c++

Question

Im trying to learn how to use JSON and Qt i have menaged and im having problem getting QJsonDocument from a file.The file opens correctly i can also see file's content with qDebug() but the QJsonDocument created from this file is always empty
if(stdButton==QDialogButtonBox::Ok)
{
qDebug()<<"accept button clicked";
QFile userList;
userList.setFileName("users.json");
userList.open(QIODevice::ReadOnly);
//using this qDebug i'm able to see files content
qDebug()<<QJsonDocument::fromJson(userList.readAll());
//but this QJsonDocument is always empty
QJsonDocument userDoc;
userDoc=QJsonDocument::fromJson(userList.readAll());
if(userDoc.isEmpty())
{
qDebug()<<"userDoc is empty";
}
qDebug()<<userDoc;
accept();
}

Answer 1

//but this QJsonDocument is always empty
QJsonDocument userDoc;
userDoc=QJsonDocument::fromJson(userList.readAll());
That's because there is nothing to read from the file since you have read everything from it in the previous call to readAll().
You can store the data from userList.readAll() and use it repeatedly.
QFile userList;
userList.setFileName("users.json");
userList.open(QIODevice::ReadOnly);
QByteArray data = userList.readAll();
qDebug()<<QJsonDocument::fromJson(data);
QJsonDocument userDoc;
userDoc=QJsonDocument::fromJson(data);