通过指向派生类的基本指针增强序列化 [英] Boost Serialization via base pointer to derived class
问题描述
可能重复:
使用多态档案进行加速序列化
我试图使用指向派生类的基指针来序列化我的类，但这仅序列化基类.
我刚刚阅读了 http://www.boost.org/doc/libs/1_32_0/libs/serialization/doc/special.html#registration ，但是导出宏和注册函数似乎都没有改变.
请考虑以下非常基本的类层次结构:
#include <iostream>
#include <fstream>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>
class A
{
private:
friend class boost::serialization::access;
template <typename Archive>
void serialize(Archive& ar, const unsigned int version)
{
std::cout << "A!\n";
}
};
class B : public A
{
private:
friend class boost::serialization::access;
template <typename Archive>
void serialize(Archive& ar, const unsigned int version)
{
ar & boost::serialization::base_object<A>(*this);
std::cout << "B!\n";
}
};
int main()
{
std::ofstream of("mybin.bin");
boost::archive::binary_oarchive oa(of);
A* b = new B();
oa << b;
delete b;
return 0;
}
输出将是:
A！
很显然，我要查找的输出是A！ B !.有什么办法可以实现?
编辑:好，在查看注释中的相关条目之后，这就是发生的情况.
有3件事需要更改:
- A类应该具有虚函数，以便被认为是多态的
- 需要导出派生类. BOOST_CLASS_EXPORT(B)
- oa<< b而不是oa<< * b
它与标准的binary_oarchive以及polymorphic_binary_oarchive一起使用.
EDIT2 :当我说b.cpp(.h)和main.cpp时，BOOST_CLASS_EXPORT产生重复的符号:
重复符号boost :: archive :: detail :: extra_detail :: init_guid :: g
我必须承认我对这个boost软件包不熟悉，但是我复制并编译了代码，产生了与上述OP相同的结果
意识到我们正在使用多态性，我在class A中添加了public: virtual ~A(){};.另外，根据文档，在main中添加了oa.register_type<B>();，输出变为:
A!
B!
根据规范，仅当declares or
inherits a virtual function时，类才是polymorphic class.对于非多态分类，也许多态只是行不通.
将BOOST_CLASS_EXPORT(B);放入B.cpp而不是B.h似乎可以解决重新定义的问题.
检查了BOOST_CLASS_EXPORT(B)的扩展结果(重新格式化):
namespace boost {
namespace serialization {
template<> struct guid_defined<B> : boost::mpl::true_ {};
template<> inline const char * guid<B>(){ return "B"; }
}
}
namespace boost {
namespace archive {
namespace detail {
namespace { // NOTE
template<> struct init_guid< B > {
static guid_initializer< B > const & g;
};
guid_initializer< B > const & init_guid< B >::g = ::boost::serialization::singleton< guid_initializer< B > >::get_mutable_instance().export_guid();
}
}
}
}
对于标记为NOTE的行:对于boost 1.42，使用了一个匿名名称空间，如果将其放入多个cpp文件或头文件中(使用g ++在ubuntu中进行测试，使用boost软件包随Ubuntu一起提供).但是，在boost 1.48中，使用了namespace extra_detail，当将其放入多个cpp文件时(使用从首页下载的boost在VS2010中在Windows中进行测试)会导致问题.
Possible Duplicate:
Boost Serialization using polymorphic archives
I am trying to serialize my classes using a base pointer to a derived class, but that only serializes the base class.
I just read http://www.boost.org/doc/libs/1_32_0/libs/serialization/doc/special.html#registration, but both the export macro and the register function didn't seem to change anything.
Consider the following, very basic, class hierarchy:
#include <iostream>
#include <fstream>
#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>
class A
{
private:
friend class boost::serialization::access;
template <typename Archive>
void serialize(Archive& ar, const unsigned int version)
{
std::cout << "A!\n";
}
};
class B : public A
{
private:
friend class boost::serialization::access;
template <typename Archive>
void serialize(Archive& ar, const unsigned int version)
{
ar & boost::serialization::base_object<A>(*this);
std::cout << "B!\n";
}
};
int main()
{
std::ofstream of("mybin.bin");
boost::archive::binary_oarchive oa(of);
A* b = new B();
oa << b;
delete b;
return 0;
}
Output will be:
A!
Clearly, the output I'm looking for is A! B!. Is there any way this can be achieved ?
EDIT: Ok, after looking at the related entry in the comments, here is what is going on.
There was 3 things to change:
- class A should have a virtual function so that it is considered polymorphic
- need to export derived classes. BOOST_CLASS_EXPORT(B)
- oa << b instead of oa << *b
It works with a standard binary_oarchive, as well as the polymorphic_binary_oarchive.
EDIT2: When I have let's say b.cpp(.h) and main.cpp, the BOOST_CLASS_EXPORT results in duplicate symbols:
duplicate symbol boost::archive::detail::extra_detail::init_guid::g
I must admit I am not familiar with this boost package, but I copied and compiled the code, which produced the same result as the OP mentioned
Realizing that we are using polymorphism, I added a public: virtual ~A(){}; in class A. Also, oa.register_type<B>(); is added in main according to the document, and output became:
A!
B!
According to the specification, a class is a polymorphic class only when declares or
inherits a virtual function. For non-polymorphic classed, maybe polymorphism just does not work.
EDIT:
Putting the BOOST_CLASS_EXPORT(B); in B.cpp instead of B.h seems to solve this problem of redefinition.
EDIT:
Checked the expansion result of BOOST_CLASS_EXPORT(B) (reformatted):
namespace boost {
namespace serialization {
template<> struct guid_defined<B> : boost::mpl::true_ {};
template<> inline const char * guid<B>(){ return "B"; }
}
}
namespace boost {
namespace archive {
namespace detail {
namespace { // NOTE
template<> struct init_guid< B > {
static guid_initializer< B > const & g;
};
guid_initializer< B > const & init_guid< B >::g = ::boost::serialization::singleton< guid_initializer< B > >::get_mutable_instance().export_guid();
}
}
}
}
And for the line marked with NOTE: for boost 1.42 used an anonymous namespace is used, which will be no problem if it is put into multiple cpp files or put into a header file (tested in ubuntu with g++, using the boost package come along with Ubuntu). However, in boost 1.48, namespace extra_detail is used, which would cause problems when put into multiple cpp files (tested in windows with VS2010, using boost downloaded from homepage).
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