C++ QT 记录仪 object

Question

I am trying to create a globally accessible object (but I am not sure if creating a global object is a good solution) which will log to file my output stream. I would like it to work similar to std::cout, but with the difference that it would log to file.

class Logger
{
    QFile* file;
    QTextStream* stream;

public:
    Logger(QString filePath);
    {
        file = new QFile(filePath);
        if(file.open(QIODevice::ReadWrite)
            stream = new QTextStream(file);
    }
    QTextStream* Log()
    {
        return stream;
    }
};


int main(int argc, char *argv[])
{
    QString filePath="Logs.txt";
    Logger l(filePath);
    MyProgram a(argc, argv);
    return a.exec();
}

In case it would be global, all I would have to do is l.Log()<<"text I want to log in" . I would prefer it to work like Log() << "text I want to log in" , but any solution would be useful: :)

I want to also mention that I have came into a logger solution on web already, but it includes creating a temporary object - in my case constantly opening and closing file each time I want to log some text is not a solution. (unless this object would use some globally open file)

Answer 1

What you need is Singleton Design Pattern . In the entire program, you need only one object of your logger class. So you need to use Singleton Design Pattern and place it into a separate file and just included it in whatever you need the logger.

---

For using streaming like operators (shift operator << ), you simply need to overload it:

friend Logger& operator<<(Logger& other, QString const& message)
{
        (*other.stream) << message;
        return other;
}

---

But in the case of Logger, it's not that simple you written. A logger base requirement are:

1. Efficiently, to be fast enough in high rate logging.
2. Thread safe, to could be used in multi-threaded programs.
3. Formatting, to be used easily.
4. Log leveling, to could categorize logs.

Take a look at: qDebug() , qInfo() , qWarning() and qFatal() . My suggestion for logging libraries are:

1. Boost.Log
2. Speed Log