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.