Qt5 Tutorial QFile (Serialization II : class) - 2020

In this tutorial, we will learn how to serialize a class. This is the continuation of the previous tutorial, QFile (Serialization).

We want to serialize a class which has two members. But unlike the previous example which is serializing primitive variables, this tutorial is dealing with a class. As we may already know, we cannot do cin or cout directly on an object of a class because it does not know how to input/output from/to a class.

Therefore, operators (<< and >>) need be overloaded.

This tutorial is almost the same except those operator overloadings:

Here is the source code, main.cpp:

#include <QCoreApplication>
#include <QFile>
#include <QDataStream>
#include <QString>
#include <QDebug>

class Student
{
public:
    int ID;
    QString Name;

    // ostream, << overloading
    friend QDataStream &Student;::operator<<(QDataStream &out;, const Student &s;)
    {
        out << s.ID << s.Name;
        return out;
    }

    // istream, >> overloading
    friend QDataStream &Student;::operator>>(QDataStream &in;, Student &s;)
    {
        s = Student();
        in >> s.ID >> s.Name;
        return in;
    }
};

void Save()
{
    Student s1;
    s1.ID = 1;
    s1.Name = "Ravel";

    Student s2;
    s2.ID = 2;
    s2.Name = "Schonberg";

    QString filename = "C:/Qt/Test/st.txt";
    QFile file(filename);

    if(!file.open(QIODevice::WriteOnly))
    {
        qDebug() << "Could not open " << filename;
        return;
    }

    QDataStream out(&file;);
    out.setVersion(QDataStream::Qt_5_1);

    out << s1 << s2;

    file.flush();
    file.close();
}

void Load()
{
    Student s1;
    Student s2;
    s2.ID;
    s2.Name;

    QString filename = "C:/Qt/Test/st.txt";
    QFile file(filename);

    if(!file.open(QIODevice::ReadOnly))
    {
        qDebug() << "Could not open " << filename;
        return;
    }

    QDataStream in(&file;);
    in.setVersion(QDataStream::Qt_5_1);

    in >> s1 >> s2;

    file.close();

    qDebug() << s1.Name << "'s ID is " << s1.ID;
    qDebug() << s2.Name << "'s ID is " << s2.ID;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    
    Save();
    Load();

    return a.exec();
}

After we read it back, we get the output like this:

"Ravel" 's ID is  1
"Schonberg" 's ID is  2

Great!

Successful class serialization.

For more on operator overloading, please visit my C++ tutorial, Operator Overloading.