遵循此问题:提升序列化子类我正在尝试支持使用 boost 序列化生成的存档的向前兼容性,但我在使用旧代码读取较新的存档时遇到问题:
class A {
public:
A() {}
virtual ~A() = default;
private:
friend class boost::serialization::access;
template <class Archive> void serialize(Archive &ar, const unsigned int version) {
ar &mAttributeFromA;
}
std::string mAttributeFromA = "mAttributeFromA";
};
BOOST_CLASS_VERSION(A, 0)
class B : public A {
public:
B() {}
private:
friend class boost::serialization::access;
template <class Archive> void serialize(Archive &ar, const unsigned int version)
{
ar &boost::serialization::base_object<A>(*this);
ar &mAttributeFromB;
if (version == 1)
ar &mNewAttribute;
}
std::string mAttributeFromB = "mAttributeFromB";
std::string mNewAttribute = "mNewAttribute";
};
BOOST_CLASS_VERSION(B, 1)
class Manager {
public:
boost::ptr_vector<A> mListOfA; // can store A or B
private:
friend class boost::serialization::access;
template <class Archive> void serialize(Archive &ar, const unsigned int /*version*/) { ar &mListOfA; }
};
BOOST_CLASS_VERSION(Manager, 0)
int main() {
Manager mgr;
mgr.mListOfA.push_back(new B);
mgr.mListOfA.push_back(new B);
std::ofstream ofs("myFile.txt");
{
boost::archive::text_oarchive oa(ofs);
oa << mgr;
}
try {
Manager mgr2;
std::ifstream ifs("myFile.txt");
boost::archive::text_iarchive ia(ifs);
ia >> mgr2;
mgr2.mListOfA.at(0);
} catch(boost::archive::archive_exception e)
{
e.what();
}
}
BOOST_CLASS_EXPORT(A)
BOOST_CLASS_EXPORT(B)
这将生成以下存档:
22 serialization::archive 13 0 0 0 0 2 3 1 B 1 1
0 1 0
1 15 mAttributeFromA 15 mAttributeFromB 13 mNewAttribute 3
2
3 15 mAttributeFromA 15 mAttributeFromB 13 mNewAttribute
如果我尝试使用相同的代码重新加载存档,一切正常。
但是,如果我尝试使用旧版本的代码加载存档:(类版本为 0,mNewAttribute 消失了)
class B : public A {
public:
B() {}
private:
friend class boost::serialization::access;
template <class Archive> void serialize(Archive &ar, const unsigned int version)
{
ar &boost::serialization::base_object<A>(*this);
ar &mAttributeFromB;
}
std::string mAttributeFromB = "mAttributeFromB";
};
BOOST_CLASS_VERSION(B, 0)
反序列化给我一个"输入流错误"
在科里鲁
如何使用旧代码反序列化新存档?
--编辑--奇怪的是,如果我在管理器中添加 A 和 B 对象,它就可以工作了。但是只有 A 或只有 B 失败...
您的类型不是多态的。版本控制可能与事情无关。
-
http://www.boost.org/doc/libs/1_60_0/libs/serialization/doc/serialization.html#derivedpointers
事实证明,序列化的对象类型取决于基类(在本例中为 base)是否为多调类。如果 base 不是多态的,也就是说,如果它没有虚函数,则将序列化 base 类型的对象。任何派生类中的信息都将丢失。如果这是想要的(通常不是),那么不需要其他努力。
您可以轻松验证这一点:向量仅反序列化A
s:
住在科里鲁
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/version.hpp>
class A {
public:
A(){}
private:
friend class boost::serialization::access;
template <class Archive> void serialize(Archive &ar, const unsigned int version) { ar &mAttributeFromA; }
std::string mAttributeFromA = "mAttributeFromA";
};
BOOST_CLASS_VERSION(A, 0)
class B : public A {
public:
B(){}
private:
friend class boost::serialization::access;
template <class Archive> void serialize(Archive &ar, const unsigned int version) {
ar &mAttributeFromB;
if (version == 1)
ar &mNewAttribute;
}
std::string mAttributeFromB = "mAttributeFromB";
std::string mNewAttribute = "mNewAttribute";
};
BOOST_CLASS_VERSION(B, 1)
#include <boost/ptr_container/serialize_ptr_vector.hpp>
class Manager {
public:
boost::ptr_vector<A> mListOfA; // can store A or B
private:
friend class boost::serialization::access;
template <class Archive> void serialize(Archive &ar, const unsigned int /*version*/) { ar &mListOfA; }
};
BOOST_CLASS_VERSION(Manager, 0)
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <sstream>
int main() {
using namespace boost;
std::stringstream ss;
{
archive::text_oarchive oa(ss);
Manager mgr;
mgr.mListOfA.push_back(new A);
mgr.mListOfA.push_back(new B);
oa << mgr;
}
std::cout << ss.str() << "n";
{
archive::text_iarchive ia(ss);
Manager mgr;
ia >> mgr;
std::cout << "Deserialized: " << mgr.mListOfA.size() << "n";
}
}
指纹
22 serialization::archive 13 0 0 0 0 2 2 1 0
0 15 mAttributeFromA 2
1 15 mAttributeFromA
Deserialized: 2
溶液:
- 使层次结构实际上具有多态性
- 添加基对象的序列化
- 注册派生类型
- ???
- 利润!
样品 (WIP) https://www.livecoding.tv/sehe/
住在科里鲁
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/base_object.hpp>
#include <boost/serialization/export.hpp>
#include <boost/serialization/version.hpp>
class A {
public:
A(){}
virtual ~A() = default;
private:
friend class boost::serialization::access;
template <class Archive> void serialize(Archive &ar, const unsigned int version) {
ar &mAttributeFromA;
}
std::string mAttributeFromA = "mAttributeFromA";
};
BOOST_CLASS_VERSION(A, 0)
class B : public A {
public:
B(){}
private:
friend class boost::serialization::access;
template <class Archive> void serialize(Archive &ar, const unsigned int version)
{
ar &boost::serialization::base_object<A>(*this);
ar &mAttributeFromB;
if (version == 1)
ar &mNewAttribute;
}
std::string mAttributeFromB = "mAttributeFromB";
std::string mNewAttribute = "mNewAttribute";
};
BOOST_CLASS_VERSION(B, 1)
BOOST_CLASS_EXPORT(A)
BOOST_CLASS_EXPORT(B)
#include <boost/ptr_container/serialize_ptr_vector.hpp>
class Manager {
public:
boost::ptr_vector<A> mListOfA; // can store A or B
private:
friend class boost::serialization::access;
template <class Archive> void serialize(Archive &ar, const unsigned int /*version*/) { ar &mListOfA; }
};
BOOST_CLASS_VERSION(Manager, 0)
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <sstream>
int main() {
using namespace boost;
std::stringstream ss;
{
archive::text_oarchive oa(ss);
Manager mgr;
mgr.mListOfA.push_back(new A);
mgr.mListOfA.push_back(new B);
oa << mgr;
}
std::cout << ss.str() << "n";
{
archive::text_iarchive ia(ss);
Manager mgr;
ia >> mgr;
std::cout << "Deserialized: " << mgr.mListOfA.size() << "n";
}
}
指纹
22 serialization::archive 13 0 0 0 0 2 2 1 0
0 15 mAttributeFromA 3 1 B 1 1
1
2 15 mAttributeFromA 15 mAttributeFromB 13 mNewAttribute
Deserialized: 2
标准提升存档(包括二进制文件)不支持向前(向上)兼容性。
有一个 xml 存档的补丁(5 年前提出,仍然不包括在内),它允许部分向前兼容 - 跳过未知字段。
有一个实验性的3rdaprty ptree存档,它也支持添加新字段。
启用二进制存档的向前兼容性将需要对其进行重大修改。
Google 协议缓冲区提供开箱即用的向前兼容性。