Boost 序列化不适用于 shared_ptr<int>

Question

下面的代码编译得很好：

#include <boost/serialization/shared_ptr.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <sstream>
#include <memory>

struct A {
    int i;

    A(): i(0) {}
    A(int i): i(i) {}

    template <typename Archive>
    void serialize(Archive& ar, const unsigned int) {
        ar & i;
    }
};

int main() {
    auto a = std::make_shared<A>(465);
    std::stringstream stream;
    boost::archive::text_oarchive out{stream};
    out << a;
}

现在我希望如果我用 int 替换 A 那么它应该也能工作。

#include <boost/serialization/shared_ptr.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <sstream>
#include <memory>

int main() {
    auto a = std::make_shared<int>(465);
    std::stringstream stream;
    boost::archive::text_oarchive out{stream};
    out << a;
}

但是，此代码无法编译，但会给出断言失败：

In file included from main.cpp:1:    
/usr/local/include/boost/serialization/shared_ptr.hpp:277:5: error: static_assert failed "boost::serialization::tracking_level< T >::value != boost::serialization::track_never"
    BOOST_STATIC_ASSERT(
    ^
...

我是不是做错了什么或者这是 Boost 中的错误？

Answer 1

来自围绕该断言的 Boost 源代码：

// The most common cause of trapping here would be serializing
// something like shared_ptr<int>.  This occurs because int
// is never tracked by default.  Wrap int in a trackable type
BOOST_STATIC_ASSERT((tracking_level< T >::value != track_never));

基本上，为了正确地序列化 shared_ptr 之类的东西，需要在序列化过程中集中跟踪指向的对象（以识别何时多个指针指向同一个对象，因此它们不会t 导致对象的两个副本被序列化）。不过，跟踪一个对象比不跟踪它的成本更高，因此不跟踪原始类型（假设会有 lot 个）。本质上，这使得在不破坏 Boost 源的情况下无法序列化 shared_ptr<primitive_type>。正如评论所说，解决方案是序列化一些 UDT containing an int.

Boost 序列化不适用于 shared_ptr<int>

Boost serialization doesn't work with shared_ptr<int>

c++

boost

boost-serialization