C++ Boost - serialization of class containing class-hierarchy objects - c++

Question

I have a class A, which contains the object of class B and I want to serialize it. The problem is, the class C inherits from B, so A can contain an object of either B or C. How can I efficiently implement the serialization with Boost?
My attempt is below, but I'm getting the error when trying to serialize A with C object, while with B it works correctly. Do you know, what am I doing wrong?
I've found some information about class-hierarchy objects serialization here, but it requires an explicit registration of the type in text_iarchive, whereas I need it to be registered in the A class because I'm not directly serializing B objects.
My attempt:
#include <fstream>
#include <iostream>
#include <vector>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
class B {
friend class boost::serialization::access;
private:
template<class Archive>
void save(Archive & ar, const unsigned int version) const {
ar & this->v->size();
for(int i = 0; i < this->v->size(); i++) {
ar & (*(this->v))[i];
}
};
template<class Archive>
void load(Archive & ar, const unsigned int version) {
size_t size;
int tmp;
ar & size;
this->v = new std::vector<int>(size);
for(int i = 0; i < size; i++) {
ar & tmp;
(*this->v)[i] = tmp;
}
}
BOOST_SERIALIZATION_SPLIT_MEMBER()
protected:
std::vector<int>* v;
public:
B();
B(std::vector<int>* v);
virtual void print_vals();
};
B::B() {
this->v = nullptr;
}
B::B(std::vector<int>* v) {
this->v = v;
}
void B::print_vals() {
for(auto e : *(this->v)) {
std::cout << e << std::endl;
}
}
class C : public B {
friend class boost::serialization::access;
private:
int num2;
template<class Archive>
void serialize(Archive & ar, const unsigned int version){
ar & boost::serialization::base_object<B>(*this);
ar & num2;
};
public:
void print_vals() override {
for(auto e : *(this->v)) {
std::cout << e << std::endl;
}
std::cout << this->num2 << std::endl;
}
C();
C(int num2, std::vector<int>* v);
};
C::C() {
this->num2 = -1;
this->v = nullptr;
}
C::C(int num2, std::vector<int> *v) {
this->num2 = num2;
this->v = v;
}
class A {
friend class boost::serialization::access;
private:
int num;
B* b_obj;
template<class Archive>
void serialize(Archive & ar, const unsigned int version){
ar & num;
ar & b_obj;
};
public:
A();
A(int num, B* b);
void print_vals();
};
A::A() {
this->num = -1;
this->b_obj = nullptr;
}
A::A(int num, B* b) {
this->num = num;
this->b_obj = b;
}
void A::print_vals() {
std::cout << this->num << std::endl;
this->b_obj->print_vals();
}
int main() {
std::vector<int> v{1,2,3};
B b = B(&v);
A a(4, &b);
std::cout << "a:" << std::endl;
a.print_vals();
std::ofstream ofs("a.txt");
{
boost::archive::text_oarchive oa(ofs);
oa << a;
ofs.close();
}
A a2;
std::ifstream ifs("a.txt");
{
boost::archive::text_iarchive ia(ifs);
ia >> a2;
ifs.close();
}
std::cout << "a2:" << std::endl;
a2.print_vals();
C c(2, &v);
A a3(6, &c);
std::cout << "a3:" << std::endl;
a3.print_vals();
std::ofstream ofs2("a3.txt");
{
boost::archive::text_oarchive oa(ofs2);
oa << a3;
ofs.close();
}
A a4;
std::ifstream ifs2("a3.txt");
{
boost::archive::text_iarchive ia(ifs2);
ia >> a4;
ifs.close();
}
std::cout << "a4:" << std::endl;
a4.print_vals();
}
OUTPUT:
a:
4
1
2
3
a2:
4
1
2
3
a3:
6
1
2
3
2
terminate called after throwing an instance of 'boost::archive::archive_exception'
what(): unregistered class - derived class not registered or exported
Signal: SIGABRT (Aborted)

Answer 1

It turns that you have missed BOOST_CLASS_EXPORTfor derived class, i.e.
BOOST_CLASS_EXPORT(C)
Boost serialization cannot serialize pointer to derived object correctly without this macro.
You can find full working code here