title: Serializing and Deserializing C++ Objects with Non-Public Member Variables tags: #C++ #serialization —

Serializing and deserializing objects is a common requirement in many applications, allowing data to be stored or transmitted in a format that can be easily reconstructed. This process becomes slightly more complex when dealing with C++ objects that have non-public member variables. In this article, we will explore how to properly serialize and deserialize such objects.

Serialization

Serialization is the process of converting an object instance into a data format that can be persisted or transmitted. In C++, there are several libraries available for serialization, such as Boost.Serialization and Protocol Buffers. For this example, we will use the Boost.Serialization library.

To serialize a C++ object with non-public member variables, we need to provide a mechanism to access those members. One way to achieve this is by declaring serialization functions save and load as friends of the class.

#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <fstream>

class MyClass {
private:
    int privateVariable;

    friend class boost::serialization::access;
    template<class Archive>
    void serialize(Archive& ar, const unsigned int version) {
        ar & privateVariable;
    }
public:
    // ...
};

In the code snippet above, we declare the serialization functions save and load as friends of the MyClass class. This allows them to access the private member privateVariable. We then provide the implementation of the serialize function, specifying how the object should be serialized.

To serialize an instance of MyClass into a text file, we can use the boost::archive::text_oarchive class:

void serializeObject(const MyClass& obj, const std::string& filename) {
    std::ofstream ofs(filename);
    boost::archive::text_oarchive oa(ofs);
    oa << obj;
}

The serializeObject function takes an instance of MyClass and a filename, opens an output stream to the file, and creates a boost::archive::text_oarchive object to write the serialized data.

Deserialization

Deserialization is the process of reconstructing an object from a serialized form. To deserialize a C++ object with non-public member variables, we follow a similar approach as serialization.

First, declare the load function as a friend of the class and implement the serialize function:

class MyClass {
private:
    int privateVariable;

    friend class boost::serialization::access;
    template<class Archive>
    void serialize(Archive& ar, const unsigned int version) {
        ar & privateVariable;
    }
public:
    // ...

    friend void loadObject(MyClass& obj, const std::string& filename);
};

Here, we declare the load function as a friend of MyClass so it can access the private member variables. We also declare the loadObject function which will be responsible for deserialization.

To deserialize an object from a text file, we use the boost::archive::text_iarchive class:

void loadObject(MyClass& obj, const std::string& filename) {
    std::ifstream ifs(filename);
    boost::archive::text_iarchive ia(ifs);
    ia >> obj;
}

The loadObject function takes an instance of MyClass and a filename, opens an input stream from the file, and creates a boost::archive::text_iarchive object to read the serialized data. It then reads the data into the provided object.

Conclusion

Serialization and deserialization of C++ objects with non-public member variables can be achieved by declaring serialization functions as friends of the classes and using serialization libraries like Boost.Serialization. By doing so, we can properly access and store the private members during serialization, and reconstruct the object during deserialization. This allows for effective persistence and transmission of data within C++ applications.