How to append json data into existing json file in Qt - c++

Question

I am creating .json file and I'm trying to append new data into json file. For that I call append file instead of writeonly file but get error at console "Error loading JSON: "garbage at the end of the document" # 548" How to append json file?
/*-------------Write data into files ------------*/
void addLogs(QString flightType, QString flightTextLogs){
QFile file("FlightNotifications.json"); // json file
file.open(QFile::WriteOnly ); // Append
QJsonObject m_projectDetails;
qint64 qiTimestamp=QDateTime::currentMSecsSinceEpoch();
QDateTime dt;
dt.setTime_t(qiTimestamp/1000);
m_projectDetails.insert("Type", flightType);
m_projectDetails.insert("TextLog", flightTextLogs);
m_projectDetails.insert("Date and Time",dt.toString("yyyy-MM-dd hh:mm:ss"));
rootObject.insert("Notifications",m_projectDetails);
rootObject1.append(rootObject);
QJsonDocument doc1(rootObject1);
file.write(doc1.toJson());
file.close();
}
/*--------------- Read json file-----------------*/
void readFlightLogs(){
qDebug()<<"Read data";
QByteArray val;
QFile file("FlightNotifications.json");
if(file.exists())
{
file.open(QIODevice:: ReadOnly | QIODevice::Text);
val = file.readAll();
file.close();
QJsonParseError jspe{};
const QJsonDocument doc = QJsonDocument::fromJson(val, &jspe);
if (doc.isNull())
{
qWarning() << "Error loading JSON:" << jspe.errorString() << "#" << jspe.offset;
}
QJsonArray jsonArray = doc.array();
if(jsonArray.size()<1)
{
}
for (int i=0; i < jsonArray.size(); i++)
{
QJsonObject temp = jsonArray.at(i).toObject();
FlightNotificationList ::getInstance()-> addAsset(temp.value("Notifications").toObject().value("Type").toString(),
temp.value("Notifications").toObject().value("TextLog").toString(),
temp.value("Notifications").toObject().value("Date and Time").toString(),
"name");
qDebug() << temp.value("Notifications").toObject().value("Type").toString();
qDebug() << temp.value("Notifications").toObject().value("TextLog").toString();
qDebug() << temp.value("Notifications").toObject().value("Date and Time").toString();
}
}
}
When I use QFile::WriteOnly the file gets override. How to append .json file

Answer 1

You should load the whole json array content, insert new item then rewrite the json array to disk.
The addLogs function could be rewritten as :
/*-------------Write data into files ------------*/
bool addLogs(QString flightType, QString flightTextLogs){
QFile file("FlightNotifications.json"); // json file
if( !file.open( QIODevice::ReadOnly ) ) //read json content
{
//open file error ...
return false;
}
QJsonDocument jsonOrg = QJsonDocument::fromJson( file.readAll() );
file.close();
//local variable, do not use m_ prefix.
QJsonObject projectDetails = { {"Type", flightType},
{"TextLog", flightTextLogs},
{"Date and Time", QDateTime::currentDateTime().toString( "yyyy-MM-dd hh:mm:ss" )} };
QJsonObject notificationObj = {{ "Notifications", projectDetails }};
QJsonArray arrLog = jsonOrg.array();
arrLog.push_back( notificationObj );
QJsonDocument doc( arrLog );
if( !file.open( QIODevice::WriteOnly ) ) //write json content to file.
{
//cannot open for write ...
return false;
}
file.write(doc.toJson());
file.close();
return true;
}

Answer 2

you should open the file in append mode too: (QIODevice::Append)
myFile.open(QIODevice::WriteOnly | ... | QIODevice::Append)