Serializing my Qt class with QDataStream

Hello, i am working on my Quizproject but recently i stumbled upon a problem.I need to serialize my Qt class.I found this example on the internet https://stackoverflow.com/questions/...zation-with-qt, it's the first answer.I want to implement it on a similar way on my class here's my class:

Code:

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class Answer{
private:
    qint8 id;
    QString answer;
 
public:
    Answer(QString nAnswer, qint8 nId);
    QString getAnswer();
    qint8 getId();
 
};
 
class Card
{
private:
    QString question;
    QVector<Answer> answers;
    qint8 solutionId;
 
public:
    Card(QString nQuestion, qint8 nSolutionId, QVector<Answer> nAnswers);
    QString getQuestion();
    QVector<Answer> getAnswers();
    qint8 getSolutionId();
 
};
 
Answer::Answer(QString nAnswer, qint8 nId)
{
    answer = nAnswer;
    id = nId;
}
 
 
Card::Card(QString nQuestion, qint8 nSolutionId, QVector<Answer> nAnswers)
{
    question = nQuestion;
    solutionId = nSolutionId;
    answers = nAnswers;
}

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So what is the problem? The StackOverflow answer tells you exactly what you need to do: implement the >> and << operators for your classes:

Code:

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QDataStream &operator<<(QDataStream &out, const Answer & answer);
QDataStream &operator>>(QDataStream &in, Answer & answer);
 
QDataStream &operator<<(QDataStream &out, const Card & card);
QDataStream &operator>>(QDataStream &in, Card & card);

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The only tricky part is how to serialize the QVector<Answer> members. The usual way is to first serialize the count (number of members in the vector), then serialize each member.

Code:

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QDataStream & operator<<( QDataSream & out, const Card & card )
{
    int nAnswers = card.getAnswers.size();
    out << nAnswers;
    foreach( answer, card.getAnswers() )
      out << answer;  // assumes you have implemented operator<< for the Answer class
 
    // do other Card data elements
 
    return out;
}

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You might find it convenient to add set...() methods to your classes (Card::setAnswers( const QVector< Answer > & answers ), etc.) because the way you have defined Card and Answer, the only way you can set these fields is in the constructor - there is no way to set them independently, for a Card or Answer instance that already exists.

You should also use references to pass or return by reference instead of by value:

Code:

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const QVector< Answer > & Card::getAnswers() const;

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The way you have implemented it, this methods makes a complete copy of the QVector before returning it. Using a reference means that no copying is done.