Passing Data From QT To C++

[physicsguy]

I was working through one of the examples on signals and slots and ive found that there is one line of code that is causing compilation issues. Here is my code

@#include <iostream>
#include <QObject>
using namespace std;

class Counter : public QObject{
Q_OBJECT
signals:
void valueChanged(int newValue);
public:
Counter(){
m_value = 1;
}
int value() const {
return m_value;
}
public slots:
void setValue(int value);
private:
int m_value;

};
void Counter::setValue(int value){
if(value != m_value){
m_value = value;
emit valueChanged(value); // This line is causing errors
}

}
int main(void){
Counter a, b;
QObject :: connect(&a, SIGNAL(valueChanged(int)), &b, SLOT(setValue(int)));

a.setValue(7);

cout << "a.setValue(7) " << endl;
cout << "(a.value, b.value) = " << a.value() << b.value() << endl;



return 0;

}@

Particularly, the error its causing is

john:~/Desktop/QT/gui1$ make
g++ -m64 -Wl,-O1 -o gui1 example1.o -L/usr/X11R6/lib64 -lQt5Gui -L/usr/lib/x86_64-linux-gnu -lQt5Core -lGL -lpthread
example1.o: In function Counter::setValue(int)': example1.cpp:(.text+0x9): undefined reference toCounter::valueChanged(int)'
collect2: error: ld returned 1 exit status
make: *** [gui1] Error 1

[SGaist]

Hi and welcome to devnet,

since you declared your QObject class in main.cpp moc is not run. Just move it to it's own header and you should be good to go

[physicsguy]

Hi,
thanks for the quick response, that was indeed the issue!

[utcenter]

SGaist - you can declare QObject derived classes in main.cpp, after your class throw in @#include "main.moc"@

So it seems the problem is not about the moc not running.