如何序列化 boost::dynamic_bitset？

Question

如何用 boost::dynamic_bitset 成员序列化一个类？

#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/dynamic_bitset.hpp>
#include <boost/serialization/bitset.hpp>
#include <sstream>

class A
{
    friend class boost::serialization::access;
    boost::dynamic_bitset<> x;
    template<class Archive>
    void serialize(Archive & ar, const unsigned int){
        ar & x;
    }
};

int main()
{
    A a;
    std::stringstream ss;
    boost::archive::text_oarchive oa(ss);
    oa << a;
    return 0;
}

编译出错（提升 1.57）

In file included from /usr/include/boost/serialization/extended_type_info_typeid.hpp:37:0,
                 from /usr/include/boost/archive/detail/oserializer.hpp:38,
                 from /usr/include/boost/archive/detail/interface_oarchive.hpp:23,
                 from /usr/include/boost/archive/detail/common_oarchive.hpp:22,
                 from /usr/include/boost/archive/basic_text_oarchive.hpp:32,
                 from /usr/include/boost/archive/text_oarchive.hpp:31,
                 from dynamic_bitset_setial.cpp:1:
/usr/include/boost/serialization/access.hpp: In static member function ‘static void boost::serialization::access::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive, T = boost::dynamic_bitset<>]’:
/usr/include/boost/serialization/serialization.hpp:69:5:   instantiated from ‘void boost::serialization::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive, T = boost::dynamic_bitset<>]’
/usr/include/boost/serialization/serialization.hpp:128:9:   instantiated from ‘void boost::serialization::serialize_adl(Archive&, T&, unsigned int) [with Archive = boost::archive::text_oarchive, T = boost::dynamic_bitset<>]’
/usr/include/boost/archive/detail/oserializer.hpp:148:5:   instantiated from ‘void boost::archive::detail::oserializer<Archive, T>::save_object_data(boost::archive::detail::basic_oarchive&, const void*) const [with Archive = boost::archive::text_oarchive, T = boost::dynamic_bitset<>]’
dynamic_bitset_setial.cpp:25:1:   instantiated from here
/usr/include/boost/serialization/access.hpp:118:9: error: ‘class boost::dynamic_bitset<>’ has no member named ‘serialize’

Answer 1

我继续 filed the pull request 为 Boost Dynamic Bitset 添加序列化支持

使用公共接口的序列化不是最佳的，因为to_block_range()/from_block_range() 需要复制m_bits（以及后续的resize()）。

我向 Boost Dynamic Bitset 添加了一个通用实现。更改干净地合并到开发或主 (1_58_0)。

变化

用

添加的实现

• 最小的干扰，只有一个嵌套的朋友 (class serialization_impl;) 已被转发声明以“锁孔”所需的朋友访问权限
• 此类以及用于 Boost 序列化的实际 ADL 挂钩在单独的标头中实现（dynamic_bitset/serialization.hpp，类似于其他支持序列化的 boost 库）。
• 这意味着存在对 Boost 序列化内容的零依赖，除非实际包含 boost/dynamic_bitset/serialization.hpp
• 实现了零拷贝（利用 std::vector<Block> 在 Boost 序列化中的内置支持）

测试

拉取请求中的第二次提交添加了对此功能的测试。我不确定如何将dyn_bitset_unit_tests5.cpp 添加到 Jamfile。我想必须做其他事情来确保链接到 Boost System 和 Boost Serialization。我已经使用一个简单的包装器自己运行了测试：

#include <modular-boost/libs/dynamic_bitset/dyn_bitset_unit_tests5.cpp>

int main() {
    test_main(0, nullptr);
}

然后可以使用例如编译和运行

g++ main.cpp -lboost_system -lboost_serialization && ./a.out

没有输出意味着没有错误。

Answer 2

dynamic_bitset<> 不可序列化，正如您所发现的（std::bitset<N> 是不同的类型）。

不过不用担心，您可以毫不费力地添加它：

namespace boost { namespace serialization {

    template <typename Ar, typename Block, typename Alloc>
        void save(Ar& ar, dynamic_bitset<Block, Alloc> const& bs, unsigned) {
            size_t num_bits = bs.size();
            std::vector<Block> blocks(bs.num_blocks());
            to_block_range(bs, blocks.begin());

            ar & num_bits & blocks;
        }

    template <typename Ar, typename Block, typename Alloc>
        void load(Ar& ar, dynamic_bitset<Block, Alloc>& bs, unsigned) {
            size_t num_bits;
            std::vector<Block> blocks;
            ar & num_bits & blocks;

            bs.resize(num_bits);
            from_block_range(blocks.begin(), blocks.end(), bs);
            bs.resize(num_bits);
        }

    template <typename Ar, typename Block, typename Alloc>
        void serialize(Ar& ar, dynamic_bitset<Block, Alloc>& bs, unsigned version) {
            split_free(ar, bs, version);
        }

} }

这有效，例如Live On Coliru

int main() {
    A a;
    for (int i=0; i<128; ++i)
        a.x.resize(11*i, i%2);

    std::stringstream ss;
    {
        boost::archive::text_oarchive oa(ss);
        oa << a;
    }
    std::cout << ss.str();
    {
        boost::archive::text_iarchive ia(ss);
        A b;
        ia >> b;

        assert(a.x == b.x);
    }
}

请注意，如果您无法复制块向量，则直接在m_bits 级别上添加序列化同样容易，但这需要进行侵入性更改（至少需要好友访问权限）。

这样的东西很容易被添加到拉取请求中。

更新added that pull request