simple signals and slots

[kroenecker]

I can't get this to compile:

#include <QApplication>
#include <QObject>
 
#include "signal.h"
 
int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
 
  MySignal a;
  MySignal b;
 
  int ret = app.exec();
 
  return ret;
}

#include <QApplication>
#include <QObject>

#include "signal.h"

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);

  MySignal a;
  MySignal b;

  int ret = app.exec();
  
  return ret;
}

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#include "signal.h"
#include <iostream>
 
MySignal::MySignal()
{}
 
MySignal::~MySignal()
{}

#include "signal.h"
#include <iostream>

MySignal::MySignal()
{}

MySignal::~MySignal()
{}

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#ifndef MYSIGNAL_H
#define MYSIGNAL_H
 
#include <QObject>
 
class MySignal : public QObject
{
 
 public:
  MySignal();
  virtual ~MySignal();
 
  void setInt(int);
 
  // signals:
  //  void send(int);
 
  // public slots:
  //  void received(int);
 
 private:
  int value;
 
};
 
#endif

#ifndef MYSIGNAL_H
#define MYSIGNAL_H

#include <QObject>

class MySignal : public QObject
{

 public:
  MySignal();
  virtual ~MySignal();

  void setInt(int);

  // signals:
  //  void send(int);

  // public slots:
  //  void received(int);

 private:
  int value;

};

#endif

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I keep getting this error:

./signal.h:6: error: invalid use of undefined type ‘struct QObject’
/usr/include/qt4/QtCore/qobjectdefs.h:164: error: forward declaration of ‘struct QObject’

[kroenecker]

This is almost too funny to be true since I've been struggling all day with QT; I think that declaring my files with the names signal.h and signal.cpp was causing the problem. I changed the names to mysignal.h and mysignal.cpp and now it compiles. There must have been some conflict there.

[Brandybuck]

I had the exact same problem yesterday morning. But the error messages were quite obscure, and it took me a couple of hours to discover the problem.