undefined reference to vtable in class

[JeanC]

Hello,

I am trying to use this code and I am getting the error 'undefined reference to `vtable for ClientHandler', on the lines indicated with << on this line
It's supposed to become a simple console program to update my dns subscriptions on namecheap and dyndns.



#include <QDebug>
#include <QNetworkAccessManager>
#include <QUrl>
#include <QNetworkRequest>
#include <QObject>

class ClientHandler : public QObject
{ // << on this line
Q_OBJECT
QNetworkAccessManager *manager;
private slots:
void replyFinished(QNetworkReply *);
public:
void CheckSite(void);
~ClientHandler();
};

void ClientHandler::replyFinished(QNetworkReply *reply) { qDebug() << "DONE"; }
ClientHandler::~ClientHandler() {} // <<-- on this line

void ClientHandler::CheckSite(void)
{
QUrl qrl("http://checkip.dyndns.org");
manager = new QNetworkAccessManager(this);
connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*)));
manager->get(QNetworkRequest(qrl));
}


Thanks for help!

[high_flyer]

This header is probably not getting moc'ed, or the moc result location is not known to the compiler.

[stampede]

No problems with compiling this code here.
Added this to header:

#include <QDebug>
#include <QNetworkAccessManager>
#include <QUrl>
#include <QNetworkRequest>
#include <QObject>

class ClientHandler : public QObject
{ // << on this line
Q_OBJECT
QNetworkAccessManager *manager;
private slots:
void replyFinished(QNetworkReply *);
public:
void CheckSite(void);
~ClientHandler();
};
This to .cpp:

void ClientHandler::replyFinished(QNetworkReply *reply) { qDebug() << "DONE"; }
ClientHandler::~ClientHandler() {} // <<-- on this line

void ClientHandler::CheckSite(void)
{
QUrl qrl("http://checkip.dyndns.org");
manager = new QNetworkAccessManager(this);
connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*)));
manager->get(QNetworkRequest(qrl));
}
Included header in main.cpp and I can use ClientHandler objects:


#include <QApplication>
#include "ClientHandler.h"
int main( int argc, char ** argv ){
QApplication app(argc,argv);
ClientHandler h;
return 0;
}

Then simply: qmake, make - compiled without errors.
Maybe try to do clean rebuild ( make clean, qmake, make ).

[JeanC]

Thanks to both of you.
Unfortunately I don't understand both of you.
@high_flyer I am rather new to Qt (played with it some years ago) so I don't understand what you mean. I am using Qt Creator so I am not used to moc.
@stampede for the life of me, I don't see what changes you made to the code. I already have a main() in there:



#include <QSettings>
#include <QDebug>
#include <QNetworkAccessManager>
#include <QUrl>
#include <QNetworkRequest>
#include <QObject>

class ClientHandler : public QObject
{
Q_OBJECT
QNetworkAccessManager *manager;
private slots:
void replyFinished(QNetworkReply *);
public:
void CheckSite(void);
~ClientHandler();
};

void ClientHandler::replyFinished(QNetworkReply *reply) { qDebug() << "DONE"; }
ClientHandler::~ClientHandler() {}

void ClientHandler::CheckSite(void)
{
QUrl qrl("http://checkip.dyndns.org");
manager = new QNetworkAccessManager(this);
connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*)));
manager->get(QNetworkRequest(qrl));
}

int main(int argc, char *argv[])
{
QSettings ini("Jean", "ddns");
if (!ini.contains("LastIp"))
{
qDebug() << "no ip";
ClientHandler c;
c.CheckSite();
}
return 0;
}

[stampede]

I have separated the code into three files: header and .cpp for the class, and third file for main() function.
As high_flyer said, the class meta code is not generated, so you are getting undefined references.
I haven't changed anything in the code itself, just when you add the class header to the list of headers in your .pro file, it gets "moc-ed", the Meta-Object code is created in moc_headerName.cpp. You don't have the header file, so this code is not generated.
Split this into three files and add header to project .pro file.
I think you can use the "moc" on your file manually, but splitting it makes more sense to me.
----
Edit:

Split this into three files and add header to project .pro file.
Add all of them to .pro file, .cpp to SOURCES and header to HEADERS

[JeanC]

Thank you, I understand.
Personally I think it's a bit overkill to use separate files for such a small program, against my taste, but if that's what Qt wants, ok.
Now I tried to add that class in Qt Creator but I can't find how. Off course I could manually edit the .pro file but it seems a bit odd that I cannot do that in Creator. If I try to edit the .pro file in Creator it just ignores my 'File Open'.

I changed things by hand, now I get:
QObject::startTimer: QTimer can only be used with threads started with QThread
and
QObject::connect: Cannot connect (null)::destroyed() to QHostInfoLookupManager::waitForThreadPoolDone()

My guess is that the class is destroyed before it can do anything. How do I avoid that? I'd like to keep this a small console program.

[stampede]

If I try to edit the .pro file in Creator it just ignores my 'File Open'.
Really ? It opens the .pro for editing when I double click it.
If you really want, you can keep it as one file:

#include <QSettings>
#include <QDebug>
#include <QNetworkAccessManager>
#include <QUrl>
#include <QNetworkRequest>
#include <QObject>

class ClientHandler : public QObject
{
Q_OBJECT
QNetworkAccessManager *manager;
private slots:
void replyFinished(QNetworkReply *);
public:
void CheckSite(void);
~ClientHandler();
};

void ClientHandler::replyFinished(QNetworkReply *reply) { qDebug() << "DONE"; }
ClientHandler::~ClientHandler() {}

void ClientHandler::CheckSite(void)
{
QUrl qrl("http://checkip.dyndns.org");
manager = new QNetworkAccessManager(this);
connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*)));
manager->get(QNetworkRequest(qrl));
}

int main(int argc, char *argv[])
{
QSettings ini("Jean", "ddns");
if (!ini.contains("LastIp"))
{
qDebug() << "no ip";
ClientHandler c;
c.CheckSite();
}
return 0;
}

#include "moc_main.cpp"
in order to get "moc_main.cpp" file you need to run "moc":

moc main.cpp -o moc_main.cpp
You don't need to add anything in the pro file this way.
And yes, your ClientHandler goes out of scope and is deleted before finishing the network request:

...
c.CheckSite();
} // c goes out of scope here

How do I avoid that?
One of possible solutions is to use QCoreApplication:


int main(int argc,char**argv){
QCoreApplication app(argc,argv);
QSettings ini("Jean", "ddns");
if (!ini.contains("LastIp"))
{
qDebug() << "no ip";
ClientHandler c;
c.CheckSite();
}
return app.exec();
}

//
void ClientHandler::replyFinished(QNetworkReply *reply) {
qDebug() << "DONE";
qApp->quit();
}

I suppose it would be better to connect to QNetworkReply signals as well, as in example from QNetworkAccessManager docs (http://doc.qt.nokia.com/latest/qnetworkaccessmanager.html#details) ,in order to handle errors.
-----
sorry, now i see the wrong code ( c was deleted anyway ), should be something like:

if (!ini.contains("LastIp"))
{
qDebug() << "no ip";
ClientHandler c;
c.CheckSite();
app.exec();
}

[JeanC]

You are a great help, thank you!

Yes indeed nothing happens if I doubleclick ddns.pro, really strange..

The project is back to one file again, turned out I had to install libqt4-dev in order to use moc.
And I used QCoreApplication, I finally understand what that's for.
Ater applying your suggestions, it now compiles, runs and even works. :)
I added some errorchecking and the cleaning up for QNetworkReply, I think it's ok.
Now I can go on! (making mistakes :) )
I'm gonna try to make that class into a blocking / synchronous method like it used to be before qt 4.6 I think.

Have a fine day!



void ClientHandler::replyFinished(QNetworkReply *reply)
{
if (reply->error() != 0)
qDebug() << "Error";
else
{
QByteArray a = reply->readAll();
qDebug() << a;
qDebug() << "DONE";
}
reply->deleteLater();
qApp->quit();
}


You are a great help, thank you!

Yes indeed nothing happens if I doubleclick ddns.pro, really strange..

The project is back to one file again, turned out I had to install libqt4-dev in order to use moc.
And I used QCoreApplication, I finally understand what that's for.
Ater applying your suggestions, it now compiles, runs and even works. :)
I added some errorchecking and the cleaning up for QNetworkReply, I think it's ok.
Now I can go on! (making mistakes :) )
I'm gonna try to make that class into a blocking / synchronous method like it used to be before qt 4.6 I think.

Have a fine day!



void ClientHandler::replyFinished(QNetworkReply *reply)
{
if (reply->error() != 0)
qDebug() << "Error";
else
{
QByteArray a = reply->readAll();
qDebug() << a;
qDebug() << "DONE";
}
reply->deleteLater();
qApp->quit();
}


Added after 39 minutes:

I made it a blocking / synchronous class:



#include <QProcess>
#include <QNetworkAccessManager>
#include <QUrl>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QObject>
#include <QCoreApplication>

class Http : public QObject
{
Q_OBJECT
QNetworkAccessManager *manager;
private slots:
void replyFinished(QNetworkReply *);
public:
bool ready;
QString Reply;
QString Get(QString);
~Http() {};
};

void Http::replyFinished(QNetworkReply *reply)
{
if (reply->error() != 0)
{
Reply = "Error";
}
else
{
Reply = reply->readAll();
}
ready = true;
reply->deleteLater();
}

QString Http::Get(QString S)
{
QUrl qrl(S);
manager = new QNetworkAccessManager(this);
connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*)));
manager->get(QNetworkRequest(qrl));
ready = false;
while (!ready)
qApp->processEvents();
return Reply;
}


Useage:



int main(int argc, char *argv[])
{
QCoreApplication app(argc,argv);
Http http;
QString S = http.Get("http://www.someurl.com");
etc.


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