Error while calling installing singleton class Qt Message Handler member function

I am trying to direct the Qt debugging messages into a text log file. while trying to install the message handler function i have written, the following error occurred:

Code:

---

main.cpp: error: C3867: 'Log::myMessageHandler': function call missing argument list; use '&Log::myMessageHandler' to create a pointer to member

---

please note that :

1. I have declared the message handler function myMessageHandler as a member function in the singleton Logger class.

2. myMessageHandler function was accessed using the[B] static method ReturnInstance().
3. The function myMessageHandler was installed in the main function of my application using qInstallMessageHanler() function.

The code is as follows:

Code:

---

/****************************Log.h***********************/    
class Log : public QObject
{
    Q_OBJECT
public:
    //class member declaration 
 
    static Log& ReturnInstance()
    {
       static Log Log_obj;   //The only Log object that will be used
       return Log_obj;
    }
    void myMessageHandler(QtMsgType type,QMessageLogContext &context,const QString &msg);
    private:
    //some member variable declartion
    QFile m_file;
 
};
/****************************Log.cpp***********************/
//constructor definition
//destructor definition
void Log::myMessageHandler(QtMsgType type, QMessageLogContext &context, const QString &msg)
{
 
QTextStream ostream(&m_file);
 
switch (type) {
case QtDebugMsg:
    ostream<<("Debugging Message: %s (%s:%u, %s)\n"  , msg, context.file, context.line, context.function);
    break;
case QtInfoMsg:
    ostream<<("Information Message: %s (%s:%u, %s)\n", msg, context.file, context.line, context.function);
    break;
case QtWarningMsg:
    ostream<<("Warnning Message: %s (%s:%u, %s)\n"   , msg, context.file, context.line, context.function);
    break;
case QtFatalMsg:
    ostream<<("Fatal Message: %s (%s:%u, %s)\n"      , msg, context.file, context.line, context.function);
    break;
case QtCriticalMsg:
    ostream<<("Critical Message: %s (%s:%u, %s)\n"   , msg, context.file, context.line, context.function);
    break;
default:
    break;
  }
}

---

And here is the installation of the message handler function:

Code:

---

#include "mainwindow.h"
#include <QApplication>
#include "logger.h"
 
int main(int argc, char *argv[])
{
    Log::ReturnInstance();         
    qInstallMessageHandler(Log::ReturnInstance().myMessageHandler);    //<------ The error
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
 
    return a.exec();
}

---

From the docs:

Quote:

---

typedef QtMessageHandler

This is a typedef for a pointer to a function with the following signature:

void myMessageHandler(QtMsgType, const QMessageLogContext &, const QString &);

---

The important words are pointer to a function, not pointer to a MEMBER function. This typically means a stand-alone function, but in your case you might be able to use a static member function of your Log class.

However, I would turn your design inside-out. Implement the message handler as a stand-alone function, but inside the handler, relay the message to the singleton's handler:

Code:

---

class Log : public QObject
{
    Q_OBJECT
public:
    //class member declaration 
 
    static Log& ReturnInstance()
    {
       static Log Log_obj;   //The only Log object that will be used
       return Log_obj;
    }
    void myMessageHandler(QtMsgType type,QMessageLogContext &context,const QString &msg);
 
    private:
    //some member variable declartion
    QFile m_file;
 
};
 
static void theMessageHandler(QtMsgType type,QMessageLogContext &context,const QString &msg)
{
    Log & log = Log::ReturnInstance();
    log.myMessageHandler( type, context, msg );
}
 
#include "mainwindow.h"
#include <QApplication>
#include "logger.h"
 
int main(int argc, char *argv[])
{
    qInstallMessageHandler( theMessageHandler );    //<------ The former error
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
 
    return a.exec();
}

---

Thanks a lot