CODEWITHSUNDEEP
jsonqt
Jared Price
Jared Price

Reputation: 5375

Qt parsing JSON using QJsonDocument, QJsonObject, QJsonArray

I'm using Qt5. I am trying to obtain values from a json object. Here is what the json object looks like that I am trying to get data from:

{
    "success": true,
    "properties": [
        {
            "ID": 1001,
            "PropertyName": "McDonalds",
            "key": "00112233445566778899aabbccddeeff"
        },
        {
            "ID": 1002,
            "PropertyName": "Burger King",
            "key": "10112233445566778899aabbccddeeff"
        },
        {
            "ID": 1003,
            "PropertyName": "Taco Bell",
            "key": "20112233445566778899aabbccddeeff"
        }
    ]
}

How can I create three arrays that contain properties[x].ID, properties[x].PropertyName, and properties[x].key in Qt?

Edit:

Using QScriptEngine I tried this:

QString data = (QString)reply->readAll();

QScriptEngine engine;

QScriptValue result = engine.evaluate(data);

qDebug() << result.toString();

Debug is saying "SyntaxError: Parse error"

Upvotes: 36

Views: 121618

Answers (3)

dave tamo
dave tamo

Reputation: 1

I'm using QT Network for my API request to Firebase but for some reason, I received a response full of data but when parsing to an array I received null.

void firebaseHandler::parseResponse(const QString &response){
    @TODO for some reason sometimes the arrayData is empty 

    QJsonDocument jsonDocument = QJsonDocument::fromJson(response.toUtf8());
    QJsonValue kind =  jsonDocument.object().value("kind");
    QJsonArray arrayData = jsonDocument.array();

     qDebug() << "json response is " << jsonDocument.toJson();
}

Upvotes: 0

Alan
Alan

Reputation: 1832

Here is an example from How To Manipulate JSON With C++ and Qt.

// reads a json file from disk to QVariantMap
// originally from http://erickveil.github.io/2016/04/06/How-To-Manipulate-JSON-With-C++-and-Qt.html
bool readJsonFile(std::string file_path, QVariantMap& result)
{
    // step 1
    QFile file_obj(QString::fromStdString(file_path));
    if (!file_obj.open(QIODevice::ReadOnly)) {
    std::cout << "Failed to open " << file_path << std::endl;
    exit(1);
    }

    // step 2
    QTextStream file_text(&file_obj);
    QString json_string;
    json_string = file_text.readAll();
    file_obj.close();
    QByteArray json_bytes = json_string.toLocal8Bit();

    // step 3
    auto json_doc = QJsonDocument::fromJson(json_bytes);

    if (json_doc.isNull()) {
        std::cout << "Failed to create JSON doc." << std::endl;
        return false;
    }
    if (!json_doc.isObject()) {
        std::cout << "JSON is not an object." << std::endl;
        return false;
    }

    QJsonObject json_obj = json_doc.object();

    if (json_obj.isEmpty()) {
        std::cout << "JSON object is empty." << std::endl;
        return false;
    }

    // step 4
    result = json_obj.toVariantMap();
    return true;
}

// writes a QVariantMap to disk
bool writeJsonFile(QVariantMap point_map, std::string file_path)
{
    QJsonObject json_obj = QJsonObject::fromVariantMap(point_map);
    QJsonDocument json_doc(json_obj);
    QString json_string = json_doc.toJson();

    QFile save_file(QString::fromStdString(file_path));
    if (!save_file.open(QIODevice::WriteOnly)) {
        std::cout << "failed to open save file" << std::endl;
        return false;
    }
    save_file.write(json_string.toLocal8Bit());
    save_file.close();
    return true;
}

Upvotes: 6

Jared Price
Jared Price

Reputation: 5375

I figured it out:

QStringList propertyNames;
QStringList propertyKeys;
QString strReply = (QString)reply->readAll();
QJsonDocument jsonResponse = QJsonDocument::fromJson(strReply.toUtf8());
QJsonObject jsonObject = jsonResponse.object();
QJsonArray jsonArray = jsonObject["properties"].toArray();

foreach (const QJsonValue & value, jsonArray) {
    QJsonObject obj = value.toObject();
    propertyNames.append(obj["PropertyName"].toString());
    propertyKeys.append(obj["key"].toString());
}

Upvotes: 78

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