Question

我正在尝试反序列化没有默认构造函数的对象。我已经看到你可以通过将存档传递给构造函数来实现这一点。但是，当我这样做时，似乎没有正确读取数据？以下是一个示例 - Works()输出＆＃34; 1 2＆＃34;应该（使用默认构造函数和运算符＆gt;＆gt;），但DoesntWork()输出＆＃34; 0 0＆＃34;。我已经介入，一切似乎都得到了适当的调用。谁能解释这两个函数之间的区别呢？

#include <fstream>

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

class Point
{
private:
    friend class boost::serialization::access;

    template<class TArchive>
    void serialize(TArchive& archive, const unsigned int version)
    {
        archive & mX;
        archive & mY;
    }

public:
    template<class TArchive>
    Point(TArchive& archive)
    {
        serialize(archive, 0);
    }

    Point(){} // Only provided to test Works()

    Point(const float x, const float y) : mX(x), mY(y) { }

    float mX = 4;
    float mY = 5;
};

void Works()
{
    std::cout << "Works():" << std::endl;
    Point p(1,2);

    std::ofstream outputStream("test.archive");
    boost::archive::text_oarchive outputArchive(outputStream);
    outputArchive << p;
    outputStream.close();

    // read from a text archive
    std::ifstream inputStream("test.archive");
    boost::archive::text_iarchive inputArchive(inputStream);
    Point pointRead;
    inputArchive >> pointRead;

    std::cout << pointRead.mX << " " << pointRead.mY << std::endl;
}

void DoesntWork()
{
    std::cout << "DoesntWork():" << std::endl;
    Point p(1,2);

    std::ofstream outputStream("test.archive");
    boost::archive::text_oarchive outputArchive(outputStream);
    outputArchive << p;
    outputStream.close();

    std::ifstream inputStream("test.archive");
    boost::archive::text_iarchive inputArchive(inputStream);
    Point pointRead(inputArchive);

    std::cout << pointRead.mX << " " << pointRead.mY << std::endl;
}

int main()
{
    Works(); // Output "1 2"
    DoesntWork(); // Output "0 0"
    return 0;
}

Answer 1

您不应该直接调用serialize方法：operator >>存档方式不仅仅是调用serialize;它取决于首先需要加载序言等的归档类型。你可以通过调试器来检查这一点，或者通过检查test.archive里面的内容，它就像

22 serialization::archive 12 0 0 1.000000000e+000 2.000000000e+000

所以在构建text_iarchive之后，对operator &的前两次调用恰好会在那里看到那些0而不是实际数据。

你的构造函数应该是：

template<class TArchive>
Point(TArchive& archive)
{
  archive >> *this;
}

编辑这是一个如何使用SFINAE来确保仍然可以调用复制构造函数的示例

Point( const Point& rh ) :
  mX( rh.mX ),
  mY( rh.mY )
{
}

template<class TArchive>
Point( TArchive& archive,
       std::enable_if_t< !std::is_same< TArchive, Point >::value >* = nullptr )
{
  archive >> *this;
}

反序列化构造函数无法正确读取数据

1 个答案: