Signal not declared in this scope/undefined reference to class::method - c++

Question

I've been trying to sort out a custom signal in my Qt application, and I can't seem to get it to compile. Essentially I have a window with a slot to handle a button press (slotCalibrate()), and another slot to receive messages and output them to the screen via a QTextEdit (slotMessage()). Both of these functions work fine in isolation.
Here is Window.cpp, slotCalibrate() is currently sending prefabricated data to Output class. In the final design slotCalibrate() will activate a calibration process on some hardware, and the results of that will be the data sent to Output.cpp
#include "window.h"
#include "output.h"
#include <QPushButton>
#include <QTextEdit>
#include <QApplication>
#include <string>
using namespace std;
Window::Window(QWidget *parent) :
QWidget(parent)
{
setFixedSize(640, 480);
calButton = new QPushButton("Calibrate", this);
calButton->setGeometry(280, 20, 80, 30);
calButton->setToolTip("Press to zero connected transducers.");
connect(calButton, SIGNAL(clicked()), this, SLOT(slotCalibrate()));
quitButton = new QPushButton("Quit", this);
quitButton->setGeometry(550, 440, 80, 30);
connect(quitButton, SIGNAL(clicked()), QApplication::instance(), SLOT(quit()));
readout = new QTextEdit(this);
readout->setReadOnly(1);
readout->setPlainText("Testing, testing, 1, 2, 3.\n");
readout->setGeometry(10, 70, 620, 360);
}
void Window::slotCalibrate()
{
string sn[5] = {"1234", "2463", "7821", "5027", "5981"};
Output *op = new Output();
op->writeMessage(1, 5, sn);
//I also tried the following with exactly the same result
//Output op;
//op.writeMessage(1, 5, sn);
}
void Window::slotMessage(string message)
{
QString qstr = QString::fromStdString(message); //Convert from string to QString
readout->append(qstr); //Print message to screen
}
I'm trying to get the button press to call the constructor of output.cpp, and then call the function writeMessage to construct and emit a message to slotMessage in window.cpp
#include "output.h"
#include <string>
#include <sstream>
using namespace std;
Output::Output(QWidget *parent) :
QWidget(parent)
{
connect (this, SIGNAL(sendMessage(string)), parentWidget(), SLOT(slotMessage(string)));
}
//void sendMessage(string)
//{
//}
void writeMessage(int cat, int count, string sn[])
{
int i;
stringstream ss;
switch (cat)
{
case 1 : //Case where calibration of one or more nodes was successful
ss << count << " transducers were successfully calibrated.\n Their serial numbers are:";
for (i=0; i<cat; i++)
{
ss << "\n" << sn[i];
}
break;
case 2: //Case where calibration of one or more nodes failed
ss << "One or more transducers failed to calibrate.";
break;
case 3: //Case where no config file is found
ss << "WARNING! Could not find 'params.config'. The default values will be used for calibration.";
break;
}
emit sendMessage(ss.str());
}
Unfortunately, with the code exactly like this, the compiler shouts at me. It says:
'sendMessage' was not declared in this scope
I have declared sendMessage in the header file as a signal, and I was under the impression signals didn't need to be implemented in code.
Nevertheless, I decided to try implementing an empty function called sendMessage. This got rid of the compiler error, but introduced another error. When calling op.writeMessage() in window.cpp, I get the error:
"undefined reference to `Output::writeMessage(int, int, std::string*)'"
I have also tried calling writeMessage inside the Output constructor, and I get the same error.
I am thoroughly lost, and have been working on this issue for a couple of days now, so any help would be immensely appreciated.
For completeness here are the header files window.h and output.h respectively:
window.h
#ifndef WINDOW_H
#define WINDOW_H
#include <QWidget>
#include <string>
class QPushButton;
class QTextEdit;
class Window : public QWidget
{
Q_OBJECT
public:
explicit Window(QWidget *parent = 0);
QTextEdit *readout;
private:
QPushButton *calButton;
QPushButton *quitButton;
signals:
public slots:
void slotCalibrate();
private slots:
void slotMessage(std::string);
};
#endif // WINDOW_H
output.h
#ifndef OUTPUT_H
#define OUTPUT_H
#include <QWidget>
#include <QObject>
#include <string>
class Output : public QWidget
{
Q_OBJECT
public:
explicit Output(QWidget *parent = 0);
void writeMessage(int, int, std::string[]);
signals:
void sendMessage(std::string);
public slots:
};
#endif // OUTPUT_H

Answer 1

Of course this does not work. You defined the writeMessage() function but you defined it as a global function. You must prepend an "Output::" to the definition.