How to change values in a json file? - c++

Question

I have the following JSON-file :
{
"users":[
{"nom":"123",
"name":"John",
"family":"ala",
"cash":1000
}
,{"nom":"456",
"name":"Joe",
"family":"ala",
"cash":1000
}
,{"nom":"131",
"name":"David",
"family":"ala",
"cash":1000
}]
}
I would like to change John's cash.
This is how I am trying to achieve this:
QFile f("file address ...");
f.open(QIODevice::ReadOnly|QIODevice::Text|QIODevice::WriteOnly);
QByteArray b=f.readAll();
QJsonDocument d=QJsonDocument::fromJson(b);
QJsonObject o=d.object();
for (int i=0;i<o["users"].toArray().size();i++) {
if(o["users"].toArray()[i].toObject()["name"].toString()=="John")
o["users"].toArray()[i].toObject()["cash"].toInt()=2000;//error unable to assign
}
However, I am getting the following error:
error: unable to assign
How to fix this?

Answer 1

Cause
You get the error, because you are trying to assign a value to the return value of a function (QJsonValue::toInt in this case).
Solution
Assign the value to QJsonValue, as demonstrated in the JSON Save Game Example:
void Character::write(QJsonObject &json) const
{
json["name"] = mName;
json["level"] = mLevel;
json["classType"] = mClassType;
}
Example
Here is an example I have written for you, in order to demonstrate how your code could be changed to implement the proposed solution:
#include <QApplication>
#include <QJsonDocument>
#include <QJsonObject>
#include <QJsonArray>
#include <QFile>
#include <QDebug>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QFile file("data.json");
if (file.open(QFile::ReadOnly | QFile::Text)) {
QJsonObject json = QJsonDocument::fromJson(file.readAll()).object();
QJsonArray users = json["users"].toArray();
file.close();
for (auto user : users) {
QJsonObject userObj = user.toObject();
if (userObj["name"].toString() == "John")
userObj["cash"] = 2000;
user = userObj;
}
qDebug() << users;
}
return a.exec();
}
Result
The given example produces the following result:
QJsonArray([{"cash":2000,"family":"ala","name":"John","nom":"123"},{"cash":1000,"family":"ala","name":"Joe","nom":"456"},{"cash":1000,"family":"ala","name":"David","nom":"131"}])
Please note, that the cash for John is set to 2000.