unregister derived class exception when split design files

[wodadehencou]

I create a simple derived class example for serialization. The difference between example in document is that I split all files.
The whole example project is https://github.com/wodadehencou/boost-serialize-derived
And build can be rerun using

cmake -B build -S . -D CMAKE_BUILD_TYPE=Debug -D CMAKE_EXPORT_COMPILE_COMMANDS=tru
e
cmake --build build
./build/src/main

The wrong output is

terminate called after throwing an instance of 'boost::archive::archive_exception'
  what():  unregistered class - derived class not registered or exported
fish: Job 1, 'build/src/main' terminated by signal SIGABRT (Abort)

If I concat all files together in a single main.cpp, everything goes right.

I follow the instruction as in Document

1. first create Base class
   1. make virtual ~Base() as virtual
   2. add serialize method to do nothing
   3. add BOOST_SERIALIZATION_ASSUME_ABSTRACT(Base) at the bottom of Base.h

#pragma once

#include "boost/serialization/access.hpp"
#include "boost/serialization/assume_abstract.hpp"

// 基类声明
class Base {
public:
  virtual void print() const = 0;
  virtual ~Base() = default;

private:
  friend class boost::serialization::access;

  template <class Archive>
  void serialize(Archive &ar, const unsigned int version) {
    // 基类无数据成员需要序列化
  }
};

BOOST_SERIALIZATION_ASSUME_ABSTRACT(Base)

2. Then create DerivedA and DerivedB public derived from Base
   1. public derive
   2. add serialize method which calls base ar &boost::serialization::base_object<Base>(*this);
   3. add BOOST_CLASS_EXPORT_KEY(DerivedA) in DerivedA.h
   4. add BOOST_CLASS_EXPORT_IMPLEMENT(DerivedA) as the first line of DerivedA.cpp

#pragma once

#include "Base.h"
#include "boost/serialization/base_object.hpp"
#include "boost/serialization/export.hpp"

// 派生类 A
class DerivedA : public Base {
public:
  DerivedA() = default;
  DerivedA(int x) : data(x) {}
  virtual ~DerivedA() = default;

  void print() const override;

private:
  int data = 0;

  friend class boost::serialization::access;

  template <class Archive>
  void serialize(Archive &ar, const unsigned int version) {
    ar &boost::serialization::base_object<Base>(*this);
    ar & data;
  }
};

BOOST_CLASS_EXPORT_KEY(DerivedA)

#include "DerivedA.h"
#include "boost/serialization/export.hpp"
#include <iostream>

BOOST_CLASS_EXPORT_IMPLEMENT(DerivedA)

void DerivedA::print() const { std::cout << "DerivedA: " << data << std::endl; }

3. Last, I create main.cpp and include Base.h, DerivedA.h, DerivedB.h, create a vector of std::unique_ptr. All serialization can not run successfully.

#include "Base.h"
#include "DerivedA.h"
#include "DerivedB.h"
#include <boost/archive/polymorphic_text_iarchive.hpp>
#include <boost/archive/polymorphic_text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/serialization/export.hpp>
#include <boost/serialization/unique_ptr.hpp>
#include <boost/serialization/vector.hpp>
#include <fstream>
#include <vector>

// BOOST_CLASS_EXPORT_IMPLEMENT(DerivedA)
// BOOST_CLASS_EXPORT_IMPLEMENT(DerivedB)

int main() {

  // 创建多态对象集合
  std::vector<std::unique_ptr<Base>> original;
  original.emplace_back(new DerivedA(42));
  original.emplace_back(new DerivedB("hello"));
  original.emplace_back(new DerivedA(100));

  // 序列化到文件
  {
    std::ofstream ofs("archive.txt");
    boost::archive::text_oarchive oa(ofs);
    oa << original; // 自动处理多态指针
  }

  // 从文件反序列化
  std::vector<std::unique_ptr<Base>> restored;
  {
    std::ifstream ifs("archive.txt");
    boost::archive::text_iarchive ia(ifs);
    ia >> restored; // 自动重建正确类型
  }

  // 验证反序列化结果
  for (const auto &ptr : restored) {
    ptr->print();
  }

  return 0;
}