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?
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