I'm compiling very simple code and as output I receive error:
`../untitled6/main.cpp:17:1: error: unable to find string literal operator 'operator"" __FILE__'
connect(&d_t, SIGNAL(timeout()), this, SLOT(doPlay()));`
The code is following:
#include <QObject>
#include <QTimer>
class Test : public QObject
{
Q_OBJECT
public:
explicit Test(QObject *parent = 0) : QObject(parent) {}
void Play()
{
connect(&d_t, SIGNAL(timeout()), this, SLOT(doPlay()));
}
public slots:
void doPlay() {}
private:
QTimer d_t;
};
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
Test test;
test.Play();
return a.exec();
}
It is happened only if I include c++11 support in my project. Without this support the compilation is Okey. I have read about user-defined literals and whitespace for gcc ver. 4.7 when c++11 support is included. But my code doesn't include any FILE code.... I found that problem is related to SIGNAL and SLOT constructions. But I have no idea what is wrong here...
P.S. For compilation I use sh4-linux-g++ (GCC) 4.8.
I have found that this issue don't observed for release build configuration. It seems it is issue for debug build configuration...
This has been fixed in Qt 4.8.1:
https://bugreports.qt.io/browse/QTBUG-22847
You should upgrade.
Related
I wrote a little program with a my own class within the main.cpp. Here the code:
#include <QApplication>
#include <QPushButton>
#include <QLabel>
class MyWidget : public QWidget {
//Q_OBJECT
public:
MyWidget(QWidget* parent = 0);
QLabel* label;
QString string;
signals:
public slots:
void setTextLabel();
};
void MyWidget::setTextLabel() {
label->setText("Test");
}
MyWidget::MyWidget(QWidget* parent)
: QWidget(parent) {
}
int main(int argc, char** argv) {
QApplication app(argc, argv);
MyWidget widget;
widget.show();
return app.exec();
}
it seems work but not "completely". My slot doens't work. I suppose i have to put Q_OBJECT. BUT, doing so, I got a list of errors, like this:
undefined reference to `vtable for MyWidget'
........................................
collect2: error: ld returned 1 exit status
make: *** [mywidget] Error 1
I can I manage that? Where the problem?
Signals and slots in Qt are managed through the moc: meta object compiler. Basically, the moc generates additional C++ code for each class containing the Q_OBJECT macro in order to implement effectively the signals and slots mechanisms. The additional code is then linked to the original class declaration.
The problem here is that your class is declared in main.cpp: this conflicts with how the moc is working with your code. You should declare your class in a separate header.
More about the moc
Edit: as hyde pointed, an alternative is to include in your cpp the file generated by the moc: Why is important to include “.moc” file at end of a Qt Source code file?
just append the line #include"main.moc" to your cpp source file should be enough.
More information:
Why is important to include ".moc" file at end of a Qt Source code file?
Question: Is there a way to check at compile-time if qRegisterMetaType<T>() was called for a custom type T?
The custom type T needs to be registered in Qt meta-type system in order to be used in e.g. queued connections.
If such a connection is made, and a signal triggered, the runtime warning will be shown:
QObject::connect: Cannot queue arguments of type 'T'
(Make sure 'T' is registered using qRegisterMetaType().)
This is hard to track, so I would prefer to check this at compile-time. Is that in any way possible?
(I understand that if it was possible, it would probably already be a part of Qt Framework itself, but maybe...?)
Note: I know I can check if a type was declared as metatype (Check if type is declared as a meta type system (for SFINAE)), but this doesn't solve my problem.
The code example would be:
#include <QCoreApplication>
#include <QDebug>
#include <QMetaMethod>
#include <QObject>
#include <QThread>
#include <QTimer>
struct Payload {
Payload() = default;
};
// Type is declared as metatype
Q_DECLARE_METATYPE(Payload)
class ObjectOne : public QObject {
Q_OBJECT
public:
using QObject::QObject;
void emitPayloadChanged() { Payload p; emit payloadChanged(p); }
signals:
void payloadChanged(const Payload& p);
};
class ObjectTwo : public QObject {
Q_OBJECT
public:
using QObject::QObject;
void handlePayload(const Payload& p) { qDebug() << "handling payload"; }
};
int main(int argc, char* argv[]) {
QCoreApplication app(argc, argv);
// Uncommenting the following line fixes the runtime warning
// qRegisterMetaType<Payload>();
QThread t1, t2;
ObjectOne o1;
o1.moveToThread(&t1);
ObjectTwo o2;
o2.moveToThread(&t2);
t1.start();
t2.start();
QObject::connect(&o1, &ObjectOne::payloadChanged, &o2, &ObjectTwo::handlePayload);
QTimer::singleShot(0, &o1, [&] { QMetaObject::invokeMethod(&o1, &ObjectOne::emitPayloadChanged); });
return app.exec();
}
#include "main.moc"
I am brand new to programming with Qt. I'm trying to do a simple subtraction of some values fed from an epicsQt widget called QELabel, which simply reads the value of an EPICS channel. I want to subtract values from two QELabels and print it to another QELabel. But, I'm getting 'undefined reference to' errors for these ->
MainWindow::on_qeLabel_dbValueChanged(QString const&) MainWindow::on_ShutterOpen_dbValueChanged(QString const&)
Here is the bit of mainwindow.cpp (I followed the example from this youtube video, especially after about the 15 minute mark)
void MainWindow::on_TopShutter_dbValueChanged(const QString &out)
{
double top,bottom,open;
top=ui->TopShutter->text().toDouble();
bottom=ui->BottomShutter->text().toDouble();
open=top-bottom
ui->ShutterOpen->setText(Qstring::number(open));
}
I'm using QTCreator, so I don't have the usual errors that I've been seeing in other forums. I have the slot declared in the header file, and MainWindow set as a Q_Object (this is the whole mainwindow.h file):
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
void on_qelabel_dbValueChanged(const QString &out);
void on_ShutterOpen_dbValueChanged(const QString &out);
void on_TopShutter_dbValueChanged(const QString &out);
private:
Ui::MainWindow *ui;
};
#endif //MAINWINDOW_H
Because they are short, and for completeness, here is the main.cpp, and then the .pro
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
And the FirstWeatherAlarm.pro:
#-------------------------------------------------
QT += core gui xml
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = FirstWeatherAlarm
TEMPLATE = app
SOURCES += main.cpp\
mainwindow.cpp
LIBS += -L/usr/lib64/qt5/plugins/designer -lQEPlugin
INCLUDEPATH += /home/jchavez/epicsqt/3.1.0/framework/include
HEADERS += mainwindow.h
FORMS += mainwindow.ui
Have I got everything declared right at the start of all the files? What is missing so that my slots are not right? I created the slot in the gui, using the "right-click" on my QELabel, and selecting "Go to Slot", so I should think all the formatting would be correct. As I've been editing, I've also run qmake and make clean which are other answers I've seen on forums. But nothing is working.
The problem is with two slots:
MainWindow::on_qeLabel_dbValueChanged(QString const&)
MainWindow::on_ShutterOpen_dbValueChanged(QString const&)
They are declared in MainWindow.h file and used somewhere in your project (otherwise you won't get an error).
But they are not implemented in mainwindow.cpp. You should add implementation to this file and the error will go away.
You have implementation for
void MainWindow::on_TopShutter_dbValueChanged(const QString &out)
in mainwindow.cpp, you can add implementation for two more slots. Think about slot as a function. And read more about signals/slots.
I am dealing with NI DAQmx and they define unsigned long as uInt32. I declare uInt32 array [1048*1024] in the header file and it compiles, but when I try to run it, it seems to freeze, and when I stop it, it exits with an error:
The program has unexpectedly finished.
D:\Projects\build-BlackAndWhite12bit-Desktop_Qt_5_1_1_MinGW_32bit-Debug\debug\BlackAndWhite12bit.exe exited with code -1073741571
Well, it does not say that there is not enough memory, but since I allocate 4*1048*1024 = 4,292,608 bytes, and my version is Qt Creator 2.8.1 Based on Qt 5.1.1 (MSVC 2010, 32 bit) on Win7 x64, I expect it to not have enough memory.
I found a similar question Qt Creator - calloc fails with large memory, but the only solution that works for me, would be, probably, moving to 64bit. But how do I do that? I tried to download the application from this website with the Qt 5.2.1 for Windows 64-bit (VS 2012, 556 MB) link. But when I got it, it seems to be a 32bit version configured for 64bit. Is this the one I need? Do I need OpenGL?
Is there a way to allow more memory for my current Qt version?
Any other ways to go around my problem?
Here's the .h content:
#ifndef MAIN12BITSAMPLING_H
#define MAIN12BITSAMPLING_H
#include <QMainWindow>
#include "nivision.h"
#include "nivis.h"
#include "NIDAQmx.h"
namespace Ui {
class main12bitSampling;
}
class main12bitSampling : public QMainWindow
{
Q_OBJECT
public:
explicit main12bitSampling(QWidget *parent = 0);
~main12bitSampling();
...
uInt32 ddata[1073152];
...
signals:
private slots:
private:
Ui::main12bitSampling *ui;
};
#endif // MAIN12BITSAMPLING_H
Here's the main.c:
#include "main12bitsampling.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
main12bitSampling w;
w.show();
return a.exec();
}
And here's the main12bitsampling.cpp:
main12bitSampling::main12bitSampling(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::main12bitSampling)
{
ui->setupUi(this);
mainLoop();
}
main12bitSampling::~main12bitSampling()
{
delete ui;
}
-1073741571==0xc00000fd
and c00000fd is the error code for a stack overflow.
Keeping such large arrays statically where it can end up on the stack is problematic, allocate it on the heap and you will be much better off:
QVector<uInt32> ddata;
main12bitSampling::main12bitSampling(QWidget *parent = 0)
QMainWindow(parent), ddata(1024*1048)
{
//...
}
I know similar question to this have been asked, but I haven't found an answer that fixes my problem.
I'm adapting some existing Qt code to add server functionality to a program my company uses. To that end I added a QTcpServer object to the existing dialog, call listen() and connect a slot to the newConnection emitter, like:
.h
class QConsole : public QDialog
{
Q_OBJECT
public:
void init();
public slots:
void new_Connection();
private:
QTcpServer m_Server;
}
.cpp
void QConsole::init()
{
m_Server.listen(QHostAddress::Any, 12346);
QDialog::connect(&m_Server, SIGNAL(newConnection()), this, SLOT(new_Connection()));
}
Main is:
int main( int argc, char *argv[] )
{
QApplication app(argc, argv);
QConsole * _output_window = new QConsole(desktopRect);
_output_window->init();
_output_window->show();
return app.exec();
}
new_Connection() never gets called so I can't see the relevance, but here it is:
void QConsole::new_Connection()
{
}
This works fine in that my program starts listening on the port specified and if I telnet to it a connection of sorts it made, but new_Connection() is never ever ever called!
I've seen posts on this problem dating back to 2005 so it's obviously not a new thing, but what I haven't found is a satisfactory answer to the problem (or any answer actually). This has got everyone at work stumped, even the person that has written a Qt server program. I'm guessing that there is something fundamentally wrong with the existing framework, but I have no idea what it might be.
I have been tearing my hair out for a day and a half over this, and the closes I got to success was using waitForNewConnection() which would actually return me a socket, but when I connected to the readReady() emitter, that was never fired either. So what would prevent these signals never getting called?
Please spare my sanity and help me as much as you can.
Here is a complete working example, tested using MSVC++ 2010.
This listens for a connection on port 12346, replies with "HELLO WORLD" and logs the connection to a list on the dialog.
main.cpp
#include <QtGui>
#include "console.hpp"
int main(int argc, char** argv)
{
QApplication app(argc, argv);
Console con;
con.show();
return app.exec();
}
console.hpp
#include <QtCore>
#include <QtGui>
#include <QtNetwork>
class Console : public QDialog
{
Q_OBJECT
public:
Console();
public slots:
void connection();
private:
QTcpServer mServer;
QListWidget* mConnList;
};
console.cpp
#include "console.hpp"
Console::Console() :
QDialog(),
mServer(),
mConnList(new QListWidget())
{
if (!mServer.listen(QHostAddress::Any, 12346))
qDebug() << "Error during 'listen'" << mServer.errorString();
connect(&mServer, SIGNAL(newConnection()), this, SLOT(connection()));
QVBoxLayout* mainLayout = new QVBoxLayout();
mainLayout->addWidget(mConnList);
setLayout(mainLayout);
}
void Console::connection()
{
qDebug() << "CONNECTION";
QTcpSocket* skt = mServer.nextPendingConnection();
if (!skt)
return;
mConnList->addItem(QString("%1:%2").arg(skt->peerAddress().toString()).arg(skt->peerPort()));
skt->write("HELLO WORLD!\r\n");
skt->close();
}
test.pro
TEMPLATE=app
CONFIG+=console debug
QT=core gui network
HEADERS=console.hpp
SOURCES=main.cpp console.cpp
Another working example, again on Linux, although I have coded a program using QTcpServer to run on both Linux and Windows before without a problem. If this doesn't work, surely it must be either a Qt installation or OS configuration problem. Either that or a bug in the Qt version.
~/tcp_test$ qmake --version
QMake version 2.01a
Using Qt version 4.8.6 in /usr/lib/x86_64-linux-gnu
~/tcp_test$ for file in qconsole.{h,cpp} main.cpp tcp_test.pro ; do echo -e "$file:\n"; cat $file; echo; echo; done
qconsole.h:
#include <QDialog>
#include <QTcpServer>
class QConsole : public QDialog
{
Q_OBJECT
public:
QConsole();
public slots:
void connection();
private:
QTcpServer server;
};
qconsole.cpp:
#include "qconsole.h"
QConsole::QConsole()
{
server.listen(QHostAddress::Any, 12346);
QDialog::connect(&server, SIGNAL(newConnection()), this, SLOT(connection()));
}
void QConsole::connection()
{
qDebug("got connection");
}
main.cpp:
#include <QApplication>
#include "qconsole.h"
int main( int argc, char *argv[] )
{
QApplication app(argc, argv);
QConsole * window = new QConsole();
window->show();
return app.exec();
}
tcp_test.pro:
QT = core gui network
CONFIG += debug
TARGET = tcp_test
SOURCES = main.cpp qconsole.cpp
HEADERS = qconsole.h
~/tcp_test$ ./tcp_test &
[3] 9784
~/tcp_test$ nc localhost 12346
got connection
^C