C++ Qt unable to parse JSON array correctly

Question

I am trying to parse json with Qt but I have no success. This is the ouput that I get from the server:

[{"anni":2019},{"anni":2018},{"anni":2017}]

Where that's generated from this simple php:

header('Content-Type: application/json');
echo json_encode($data);

The $data is an array containing the values you see above. I am using this piece of code in Qt 5.11.2:

void MainWindow::showYears() {   

    //reply is a QNetworkReply* reply;
    if (reply->error() != QNetworkReply::NoError) {
        //some error managment
    } else {

        auto responsedata = reply->readAll();

        QJsonArray years = QJsonDocument::fromJson(responsedata).array();          
        qDebug() << QString{responsedata};

        for(const QJsonValue& y : years) {
            QJsonObject obj = y.toObject();

            //doing "qDebug() << r" shows that r is "" (empty!)
            auto r = obj["anni"].toString();

            ui->comboBoxP->addItem(r);
        }

    }

}

What's wrong here?

Please note that qDebug() << QString{responsedata}; prints "[{\"anni\":2019},{\"anni\":2018},{\"anni\":2017}]"

Tezirg · Accepted Answer · 2018-11-01 14:46:34Z

6

The value for your field anni is an integer. Using the member function toString will not convert it to a string representation. it will return NULL. http://doc.qt.io/qt-5/qjsonvalue.html#toString

Try with: auto r = QString::number(obj["anni"].toInt());

answered Nov 1, 2018 at 14:46

Tezirg

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1 Comment

Raffaele Rossi Over a year ago

Thank you! I misunderstood the usage of toString(), I thought it was able to convert the field to a string.

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