Serializing a map of objects to xml using boost::serialization - c++

Question

The serialization example below is from the boost mailing list which is pretty much the same as what I would like to do. However, I have changed the archive so that it will serialize to XML. The compile does not fail if I serialize to binary, but it fails when serializing to xml. The compile fails in basic_xml_oarchive.hpp in the following method:
// boost code where compile fails
template<class T>
void save_override(T & t, BOOST_PFTO int)
{
// If your program fails to compile here, its most likely due to
// not specifying an nvp wrapper around the variable to
// be serialized.
BOOST_MPL_ASSERT((serialization::is_wrapper<T>));
this->detail_common_oarchive::save_override(t, 0);
}
It seems I haven't done enough to allow the std::map<int, CSomeData> object to be serialized, any ideas on how to fix this?
My serialization implementation:
#include <boost/archive/xml_oarchive.hpp>
#include <boost/archive/xml_iarchive.hpp>
#include <boost/serialization/map.hpp>
#include <fstream>
#include <string>
#include <map>
using namespace std;
// This is a test class to use as the map data.
class CSomeData {
public:
CSomeData(){};
CSomeData(float f0, string str0)
{
m_f0 = f0;
m_str0 = str0;
}
float m_f0;
string m_str0;
private:
friend class boost::serialization::access;
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & m_f0;
ar & m_str0;
}
};
// This is the class we really want to try serializing.
class CTest {
public:
CTest(){};
CTest(int nNumber)
{
m_nNumber = nNumber;
// Fill with some dummy data.
m_mTst.insert(make_pair(0, CSomeData(0.23f, "hi hi hi")));
m_mTst.insert(make_pair(1, CSomeData(7.65f, "second one")));
m_mTst.insert(make_pair(2, CSomeData(9.23f, "third one")));
m_mTst.insert(make_pair(3, CSomeData(5.6766, "chosen one")));
}
~CTest(){};
save()
{
std::ofstream ofs("filename");
// Write class instance to archive. Writing seems to work ok.
boost::archive::xml_oarchive oa(ofs);
oa << BOOST_SERIALIZATION_NVP(*this);
}
int m_nNumber;
private:
map<int, CSomeData> m_mTst;
friend class boost::serialization::access;
template<class Archive>
void serialize(Archive &ar, const unsigned int version)
{
ar & m_nNumber;
ar & m_mTst;
}
};

Answer 1

I believe you need to tag the members with a name for XML serialisation. This specifies the element name to use in the XML. I.e. use something like:
ar & BOOST_SERIALIZATION_NVP(m_f0);
or (better in this case):
ar & make_nvp("field0", my_f0);
The tags will be ignored for binary serialisation. More details here:
http://www.boost.org/doc/libs/1_43_0/libs/serialization/doc/wrappers.html