qInstallMessageHandler has a segmentation fault?

CAD_coding

In my following code, the line marked with *** creates a segmentation fault when qInstallMessageHandler() is called. If it is commented out, there is no more segmentation fault. I want to handle the logging of the messages to be done in a separate class, hence the class Logger.

Logger log;

void myMessageOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg)
{
    QStringList data;
    data.append(context.category);
    data.append(context.file);
    data.append(context.function);
    data.append(QString(context.line));
    data.append(QString(context.version));
    log.myMessageOutput(type, data, msg); //*** comment out this line to remove the segfault
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    a.setApplicationName("MyApp");
    a.setApplicationVersion("1.0.0");

    qInstallMessageHandler(myMessageOutput);
    log.turnOnDebug();
...
}

Logger.h

class Logger : public QObject
{
    Q_OBJECT
public:
    void myMessageOutput(QtMsgType type, QStringList context, const QString msg);
    explicit Logger(QObject *parent = 0);
    ~Logger();
    static Logger *get_obj() {return ptr;}
    static void turnOnDebug() {get_obj()->debugMode = true;}
    static void turnOffDebug() {get_obj()->debugMode = false;}
    static void moveLogToSession(QString sessionName);

private:
    QFile *logFile;
    QTextStream *stream;
    QMutex *mutex;
    bool debugMode;
    bool errorMsg;
    static Logger *ptr;

    void write(QString str);

signals:
    void SaveSession();
    void FatalSaveSession();

public slots:

};

In Logger.cpp

void Logger::myMessageOutput(QtMsgType type, QStringList context, const QString msg)
{
   mutex->lock();
   QString str = "";
    switch (type)
    {
        case QtDebugMsg:
        if(!debugMode)
        {
            mutex->unlock();
            return;
        }
        write(msg);
        break;

        case QtInfoMsg:
        str.append("\n*** Information ***\n");
        str.append(msg + "\n");
        str.append("Category: " + context.at(0) + "\n");
        str.append("File: " + context.at(1) + "\n");
        str.append("Function: " + context.at(2) + "\n");
        str.append("Line: " + context.at(3) + "\n");
        str.append("Version: " + context.at(4));
        str.append("\n*** Information Complete ***\n");
        write(str);
        break;

        case QtWarningMsg:
        if(!(context.at(2).contains("setGeometry")))
        {
            str.append("\n*** Warning ***\n");
            str.append(msg + "\n");
            str.append("Category: " + context.at(0) + "\n");
            str.append("File: " + context.at(1) + "\n");
            str.append("Function: " + context.at(2) + "\n");
            str.append("Line: " + context.at(3) + "\n");
            str.append("Version: " + context.at(4));
            str.append("\n*** Warning Complete ***\n");
            write(str);
            errorMsg = true;
            emit Logger::ptr->SaveSession();
        }
        break;

        case QtCriticalMsg:
        str.append("\n*** Critical ***\n");
        str.append(msg + "\n");
        str.append("Category: " + context.at(0) + "\n");
        str.append("File: " + context.at(1) + "\n");
        str.append("Function: " + context.at(2) + "\n");
        str.append("Line: " + context.at(3) + "\n");
        str.append("Version: " + context.at(4));
        str.append("\n*** Critical Complete ***\n");
        write(str);
        errorMsg = true;
        emit Logger::ptr->SaveSession();
        break;

        case QtFatalMsg:
        str.append("\n*** Fatal ***\n");
        str.append(msg + "\n");
        str.append("Category: " + context.at(0) + "\n");
        str.append("File: " + context.at(1) + "\n");
        str.append("Function: " + context.at(2) + "\n");
        str.append("Line: " + context.at(3) + "\n");
        str.append("Version: " + context.at(4));
        str.append("\n*** Fatal Complete ***\n");
        write(str);
        errorMsg = false;
        emit Logger::ptr->FatalSaveSession();
        QApplication::exit(-2);
    }
    Logger::mutex->unlock();
}

Why is Qt not allowing me to set my class as the message handler?
What is the workaround if I want to use my Logger class?

jsulm

Why do you use so many pointers (logFile, stream, mutex)? Why not just normal instance variables.
Did you initialize all these pointers?

CAD_coding

@jsulm When I created these classes I felt that pointers are best way of manipulating class variables.
Now I understand that I was incorrect.
But now I have come to a stage where I have to use pointers because I am depending on addresses of class variables.

That being said, all the variables are initialised appropriately.

jsulm

You can get the pointers to your instance variables when needed (& operator).
Did you try to debug? Maybe your logger is called when you set it and something is wrong in your code.

CAD_coding

@jsulm thanks I fixed it now. It was a stupid mistake, not setting up the static variable.