Boost序列化:前向兼容性因输入流错误而失败 [英] Boost serialization : forward compatibility fail with input stream error
问题描述
以下问题: Boost序列化子类 我试图支持通过boost序列化生成的归档文件的向前兼容性，但是我无法读取带有旧代码的新归档文件:
Following this question : Boost serialize child class I'm trying to support forward compatibility for my archive generated with boost serialization but i'm having trouble reading a newer archive with older code :
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档案，则一切正常.
If i try to reload the archive with the same code , everything works perfectly.
但是，如果我尝试使用旧版本的代码加载归档文件:(类版本为0，mNewAttribute消失了)
However if i try to load the archive with an older version of the code : (Class version is 0 and mNewAttribute is gone)
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)
反序列化向我抛出"输入流错误"
The deserialization throw me an "input stream error"
如何使用旧代码反序列化新档案?
How can i deserialize new archive with old code ?
-编辑- 奇怪的是，如果我在管理器中添加A 和 B对象，则它正在工作.但是只有A或只有B会失败...
-- Edit -- Strangely, if i add A and B objects inside the manager it's working. But fail with only A or only B ...
推荐答案
您的类型不是多态的.版本控制可能与事物无关.
Your types aren't polymorphic. Versioning likely has nothing to do with things.
事实证明，序列化的对象的类型取决于基类(在这种情况下是基类)是否是多语言的.如果base不是多态的，也就是说它没有虚函数，那么base类型的对象将被序列化.任何派生类中的信息都将丢失.如果这是所需的 (通常是不需要的) ，则不需要其他工作.
It turns out that the kind of object serialized depends upon whether the base class (base in this case) is polymophic or not. If base is not polymorphic, that is if it has no virtual functions, then an object of the type base will be serialized. Information in any derived classes will be lost. If this is what is desired (it usually isn't) then no other effort is required.
您可以轻松地验证这一点:向量仅反序列化A s:
You can verify this easily: the vector only deserializes As:
#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";
}
}
打印
22 serialization::archive 13 0 0 0 0 2 2 1 0
0 15 mAttributeFromA 2
1 15 mAttributeFromA
Deserialized: 2
解决方案:
- 使层次结构实际上是多态的
- 添加基础对象的序列化
- 注册派生类型
- ???
- 利润！
样本(WIP) https://www.livecoding.tv/sehe/
#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";
}
}
打印
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
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