Serialization with Qt

Question

I am programming a GUI with Qt library. In my GUI I have a huge std::map.

"MyType" is a class that has different kinds of fields.

I want to serialize the std::map. How can I do that? Does Qt provides us with neccesary features?

Answer 1

QDataStream handles a variety of C++ and Qt data types. The complete list is available at http://doc.qt.io/qt-4.8/datastreamformat.html. We can also add support for our own custom types by overloading the << and >> operators. Here's the definition of a custom data type that can be used with QDataStream:

class Painting { public:     Painting() { myYear = 0; }     Painting(const QString &title, const QString &artist, int year) {         myTitle = title;         myArtist = artist;         myYear = year;     }     void setTitle(const QString &title) { myTitle = title; }     QString title() const { return myTitle; }     ... private:     QString myTitle;     QString myArtist;     int myYear; }; QDataStream &operator<<(QDataStream &out, const Painting &painting); QDataStream &operator>>(QDataStream &in, Painting &painting); 

Here's how we would implement the << operator:

QDataStream &operator<<(QDataStream &out, const Painting &painting) {     out << painting.title() << painting.artist()         << quint32(painting.year());     return out; } 

To output a Painting, we simply output two QStrings and a quint32. At the end of the function, we return the stream. This is a common C++ idiom that allows us to use a chain of << operators with an output stream. For example:

out << painting1 << painting2 << painting3;

The implementation of operator>>() is similar to that of operator<<():

QDataStream &operator>>(QDataStream &in, Painting &painting) {     QString title;     QString artist;     quint32 year;     in >> title >> artist >> year;     painting = Painting(title, artist, year);     return in; } 

This is from: C++ GUI Programming with Qt 4 By Jasmin Blanchette, Mark Summerfield