Qt/C++ get Json request - c++

Question

I'm new to Qt Framework and I'm trying to get the list of earthquakes from EMSC api. My code looks like this:
void MainWindow::getJsonData(QNetworkAccessManager *mNetworkManager) {
const QUrl json("https://www.seismicportal.eu/fdsnws/event/1/query?limit=100&format=json");
QNetworkRequest *mNetworkRequest = new QNetworkRequest;
mNetworkRequest->setUrl(json);
mNetworkRequest->setRawHeader("Content-Type", "application/json");
mNetworkRequest->setRawHeader("Accept", "application/json");
QNetworkReply *mNetworkReply = mNetworkManager->get(*mNetworkRequest);
QString replyString = (QString) mNetworkReply->readAll();
QJsonDocument document = QJsonDocument::fromJson(replyString.toUtf8());
QJsonObject object = document.object();
QJsonValue type = object["type"].toString();
QJsonArray featuresArray = object["features"].toArray();
qDebug() << type;
qDebug() << featuresArray;
}
The problem is that I'm not getting any response from the server.

Answer 1

Qt is a library (not a framework) that handles all transactions asynchronously through signals and slots, so don't expect the response to be obtained synchronously.
#include <QCoreApplication>
#include <QJsonArray>
#include <QJsonDocument>
#include <QJsonObject>
#include <QNetworkAccessManager>
#include <QNetworkReply>
class Client: public QObject{
public:
void startRequest(){
const QUrl json("https://www.seismicportal.eu/fdsnws/event/1/query?limit=100&format=json");
QNetworkRequest request;
request.setUrl(json);
request.setRawHeader("Content-Type", "application/json");
request.setRawHeader("Accept", "application/json");
QNetworkReply *reply = mNetworkManager.get(request);
connect(reply, &QNetworkReply::finished, this, &Client::processRequest);
}
private:
void processRequest(){
QNetworkReply * reply = qobject_cast<QNetworkReply *>(sender());
if(!reply) return;
QJsonDocument document = QJsonDocument::fromJson(reply->readAll());
QJsonObject object = document.object();
QJsonValue type = object["type"].toString();
QJsonArray featuresArray = object["features"].toArray();
qDebug() << type << featuresArray;
reply->deleteLater();
}
QNetworkAccessManager mNetworkManager;
};
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
Client client;
client.startRequest();
return a.exec();
}
Output:
QJsonValue(string, "FeatureCollection") QJsonArray([{"geometry":{"coordinates":[16.23,45.4,-2],"type":"Point"},"id":"20210202_0000178", ...

Answer 2

Here's some of my code:
QNetworkRequest req (QUrl(QString::fromStdString(url)));
req.setHeader(QNetworkRequest::KnownHeaders::ContentTypeHeader, "application/json");
if (authHeader.length() > 0) {
req.setRawHeader(QByteArray("Authorization"), QByteArray::fromStdString(authHeader));
}
QByteArray bodyArray;
if (body.length() > 0) {
bodyArray.append(QString::fromStdString(body).toUtf8());
}
QNetworkReply * reply = method(req, bodyArray);
QObject::connect(reply, &QNetworkReply::finished, [=]{
.... });