Pass QCoreApplication in parameter - c++

Question

I'm tring to build a client for a web service. My goal is to send a request to my server every second. I used this library to help me : QHttp
I create a timer that I link with a signal to my QCoreApplication app, and send my request when the timer reach 1 second.
Here's how I do it :
main.cpp
#include "request.h"
int main(int argc, char** argv) {
QCoreApplication app(argc, argv);
Request* request = new Request();
request->sendRequestPeriodically(1000, app);
return app.exec();
}
request.h
//lots of include before
class Request
{
Q_OBJECT
public:
Request();
void sendRequestPeriodically (int time, QCoreApplication app);
public slots:
void sendRequest (QCoreApplication app);
};
request.cpp
#include "request.h"
void Request::sendRequest (QCoreApplication app){
using namespace qhttp::client;
QHttpClient client(&app);
QUrl server("http://127.0.0.1:8080/?Clearance");
client.request(qhttp::EHTTP_GET, server, [](QHttpResponse* res) {
// response handler, called when the incoming HTTP headers are ready
// gather HTTP response data (HTTP body)
res->collectData();
// when all data in HTTP response have been read:
res->onEnd([res]() {
// print the XML body of the response
qDebug("\nreceived %d bytes of http body:\n%s\n",
res->collectedData().size(),
res->collectedData().constData()
);
// done! now quit the application
//qApp->quit();
});
});
// set a timeout for the http connection
client.setConnectingTimeOut(10000, []{
qDebug("connecting to HTTP server timed out!");
qApp->quit();
});
}
void Request::sendRequestPeriodically(int time, QCoreApplication app){
QTimer *timer = new QTimer(this);
QObject::connect(timer, SIGNAL(timeout()), this, SLOT(sendRequest(app)));
timer->start(time); //time specified in ms
}
Request::Request()
{
}
I got these errors :
C:\Qt\5.7\mingw53_32\include\QtCore\qcoreapplication.h:211: erreur : 'QCoreApplication::QCoreApplication(const QCoreApplication&)' is private
Q_DISABLE_COPY(QCoreApplication)
C:\Users\ebelloei\Documents\qhttp\example\client-aircraft\main.cpp:7: erreur : use of deleted function 'QCoreApplication::QCoreApplication(const QCoreApplication&)'
I'm new to Qt, but I assume this comes from the fact I can't passe my QCoreApplication in parameters, is this right ?

Answer 1

First of all, if you need to access the global application instance, you shouldn't be passing it around. Use the qApp macro, or QCoreApplication::instance().
But that's besides the point: the QHttpClient client instance is a local variable, its lifetime managed by the compiler. There's no point to giving it a parent. The client gets destroyed right as sendRequest exits: your sendRequest is effectively a no-op because of that.
You also have errors in your connect statements: you can't pass argument values using the old style connect syntax:
// Wrong: the connection fails and does nothing.
connect(timer, SIGNAL(timeout()), this, SLOT(sendRequest(foo)));
// Qt 5
connect(timer, &QTimer::timeout, this, [=]{ sendRequest(foo); });
// Qt 4
this->foo = foo;
connect(timer, SIGNAL(timeout()), this, SLOT(sendRequest()));
// sendRequest would then use this->foo
Ideally, you should redesign your code to use QNetworkAccessManager. If not, then you must keep the QHttpClient instance alive within main:
int main(int argc, char** argv) {
QCoreApplication app(argc, argv);
qhttp::client::QHttpClient client;
auto request = new Request(&client);
request->sendRequestPeriodically(1000);
return app.exec();
}
And then:
class Request : public QObject
{
Q_OBJECT
QTimer m_timer{this};
qhttp::client::QHttpClient *m_client;
public:
explicit Request(qhttp::client::QHttpClient *client);
void sendRequestPeriodically(int time);
void sendRequest();
};
Request::Request(qhttp::client::QHttpClient *client) :
QObject{client},
m_client{client}
{
QObject::connect(&m_timer, &QTimer::timeout, this, &Request::sendRequest);
}
void Request::sendRequestPeriodically(int time) {
timer->start(time);
}
void Request::sendRequest() {
QUrl server("http://127.0.0.1:8080/?Clearance");
m_client->request(qhttp::EHTTP_GET, server, [](QHttpResponse* res) {
...
});
}

Answer 2

You can't pass a copy QCoreApplication object via its copy constructor, you have to pass a pointer to QCoreApplication.
All of "QCoreApplication app" should be replaced by "QCoreApplication *app" and calls to those functions must include a pointer to app not a copy of it.
request.h
//lots of include before
class Request
{
Q_OBJECT
public:
Request();
void sendRequestPeriodically (int time, QCoreApplication *app);
public slots:
void sendRequest (QCoreApplication *app);
};
request.cpp
#include "request.h"
void Request::sendRequest (QCoreApplication *app){
using namespace qhttp::client;
QHttpClient client(app);
QUrl server("http://127.0.0.1:8080/?Clearance");
client.request(qhttp::EHTTP_GET, server, [](QHttpResponse* res) {
// response handler, called when the incoming HTTP headers are ready
// gather HTTP response data (HTTP body)
res->collectData();
// when all data in HTTP response have been read:
res->onEnd([res]() {
// print the XML body of the response
qDebug("\nreceived %d bytes of http body:\n%s\n",
res->collectedData().size(),
res->collectedData().constData()
);
// done! now quit the application
//qApp->quit();
});
});
// set a timeout for the http connection
client.setConnectingTimeOut(10000, []{
qDebug("connecting to HTTP server timed out!");
qApp->quit();
});
}
void Request::sendRequestPeriodically(int time, QCoreApplication app){
QTimer *timer = new QTimer(this);
QObject::connect(timer, SIGNAL(timeout()), this, SLOT(sendRequest(app)));
timer->start(time); //time specified in ms
}
Request::Request()
{
}
main.cpp
#include "request.h"
int main(int argc, char** argv) {
QCoreApplication app(argc, argv);
Request* request = new Request();
request->sendRequestPeriodically(1000, &app);
return app.exec();
}
Edit
As KubaOber said, there are more issues in your code, read his answer