How to make a text file with Qt

Question

I am making a GUI application in which the user insert some information and click either an Add button to add more info, or a Finished button to finish the process. The outputs of the process are going to be 4 text files. So, I've made a class with 4 functions each of which creates one of those files:

class RequiredFilesMaker
{
public:
    RequiredFilesMaker();
    ~RequiredFilesMaker();
    void a1(float xcor, float ycor, int xnbin, int ynbin , int resolution);
    void a2();
    void a3();
    void a4();
};

Due to my initial research, I understand that I should use QTextStream to save the data to a file. But, there is an issue with using these handy objects. I can't define them in the class and initialize them in the constructor. I checked all the documentations and forums to see what other people have done. But, I found out that the only method that is widely used is to call the object inside a function and close the data file after doing the job (which is not my favorite, since I need to keep the file open for the user to write on it).

QFile data("output.txt");
if (data.open(QFile::WriteOnly | QFile::Truncate)) {
    QTextStream out(&data);
    out << "Result: " << qSetFieldWidth(10) << left << 3.14 << 2.7;
    // writes "Result: 3.14      2.7       "
}

Is there anyone who knows how to address the issue? I came up with a new idea of saving all the information inside another variable (MyMagic) and just call a function like:

void RequiredFilesMaker::a1(float b1, float b2, int b3, int b4, int b5){
    QFile gs_qfile("abc.dat");
    if (!gs_qfile.open(QIODevice::WriteOnly)){
        qDebug() <<"Couldn't open the file";
        return;
    }
    QDataStream out(&gs_qfile);
    out.setVersion(QDataStream::Qt_4_7);
    out << MyMagic;

    gs_qfile.flush();
    gs_qfile.close();

But, I am wondering about the type of MyMagic.

Answer 1

You need a singleton class which is shared across all classes and manages all logging operations.

class singletonclass{

public:
    singletonclass(){
        // Opening log file and ...
    }

    static singletonclass * getInstance(){
        static singletonclass * instance;
        if(!instance)
            instance = new singletonclass();
        return instance;
    }

    void doLog(QString log){
        // do logging
    }
}

You can use get instance method in your application to provide a global class instance :

singletonclass::getInstance()->doLog("Salam");