问Qt序列化、非成员QDataStream和operator<<

EN

QDataStream& operator<<(QDataStream& ds, SomeType const& obj)
{
  // do stuff to write obj to the stream
  return ds;
}

#include <QtCore>

class Base {
    public:
        Base() {};
        virtual ~Base() {};
    public:
        // This must be overriden by descendants to do
        // the actual serialization I/O
        virtual void serialize(QDataStream&) const = 0;
};

class Derived: public Base {
    QString member;
    public:
        Derived(QString const& str): member(str) {};
    public:
        // Do all the necessary serialization for Derived in here
        void serialize(QDataStream& ds) const {
            ds << member;
        }
};

// This is the non-member operator<< function, valid for Base
// and its derived types, that takes advantage of the virtual
// serialize function.
QDataStream& operator<<(QDataStream& ds, Base const& b)
{
    b.serialize(ds);
    return ds;
}

int main()
{
    Derived d("hello");

    QFile file("file.out");
    file.open(QIODevice::WriteOnly);
    QDataStream out(&file);

    out << d;
    return 0;
}