【发布时间】：2014-06-11 04:45:36
【问题描述】：
我正在尝试使用 boost::property_tree 反序列化 JSON 数据。我已经建立了一个 boost fusion 序列来识别结构成员元素的类型，并使用一个函数来反序列化一个适当的 JSON 树。它曾经适用于包含普通数据类型的结构。当我尝试对包含结构的结构应用相同的操作时，逻辑失败并导致编译器错误。谁能看到我哪里出错了。
#include <boost/fusion/include/sequence.hpp>
#include <boost/fusion/include/algorithm.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/adapt_adt.hpp>
#include <boost/fusion/include/is_sequence.hpp>
#include <boost/mpl/eval_if.hpp>
#include <boost/type_traits.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
#include <boost/lexical_cast.hpp>
#include <boost/foreach.hpp>
#include <type_traits>
#include <typeinfo>
#include <vector>
#include <list>
std::string type_name_to_recover = "";
template<typename type_t>
struct is_container : public std::false_type {};
template<typename type_t, typename allocator_t>
struct is_container < std::vector < type_t , allocator_t> > : public std::true_type {};
template<typename type_t, typename allocator_t>
struct is_container < std::list < type_t , allocator_t> > : public std::true_type {};
template <typename type_t>
struct simple_serializer;
template <typename sequence_t, typename index_t>
struct sequence_iterator
{
typedef typename boost::fusion::result_of::value_at<sequence_t, index_t>::type current_type_t;
typedef typename boost::mpl::next<index_t>::type next_index_t;
typedef boost::fusion::extension::struct_member_name<sequence_t, index_t::value> type_name_t;
static inline void read_json( boost::property_tree::ptree &pt, sequence_t& sequence)
{
type_name_to_recover = type_name_t::call();
simple_serializer<current_type_t>::read_json(pt, boost::fusion::at<index_t>(sequence));
type_name_to_recover = "";
sequence_iterator<sequence_t, next_index_t>::read_json(pt, sequence);
}
};
//tail of the sequence
template <typename sequence_t>
struct sequence_iterator<sequence_t, typename boost::fusion::result_of::size<sequence_t>::type >
{
static inline void read_json( boost::property_tree::ptree &pt, sequence_t& sequence) { }
};
template < typename sequence_t >
struct sequence_iterator_final : sequence_iterator < sequence_t, boost::mpl::int_< 0 > > {};
////////////////////////////////////////////////////////
//Plain old types serializer
////////////////////////////////////////////////////////
template <typename type_t>
struct serialize_pod
{
typedef serialize_pod<type_t> type;
static inline void read_json( boost::property_tree::ptree &pt, type_t& t)
{
auto v = pt.get_child(type_name_to_recover);
t = boost::lexical_cast<type_t>(v.data());
}
};
////////////////////////////////////////////////////////
//Sequence serializer
////////////////////////////////////////////////////////
template <typename sequence_t>
struct serialize_sequence
{
typedef serialize_sequence<sequence_t> type;
static inline void read_json( boost::property_tree::ptree &pt, sequence_t& sequence)
{
sequence_iterator_final<sequence_t>::read_json(pt, sequence);
}
};
////////////////////////////////////////////////////////
//Container serializer
////////////////////////////////////////////////////////
template <typename container_type_t>
struct serialize_container
{
typedef serialize_container<container_type_t> type;
template <typename type_t>
static void read_json( boost::property_tree::ptree &pt, std::vector<type_t> &t)
{
std::string temp_name = type_name_to_recover;
type_name_to_recover = "";
BOOST_FOREACH( boost::property_tree::ptree::value_type &tree_node_value, pt.get_child(temp_name) )
{
boost::property_tree::ptree subtree = (boost::property_tree::ptree) tree_node_value.second ;
if( subtree.empty() )
{
auto tree_node_y = subtree.data();
type_t type_val;
simple_serializer<type_t>::read_json(tree_node_y, type_val);
t.push_back(type_val);
}
else
{
auto tree_node_x = subtree.data();
type_t type_val;
simple_serializer<type_t>::read_json(tree_node_x, type_val);
t.push_back(type_val);
}
}
}
};
template <typename type_t>
struct resolve_serializer_type
{
typedef
typename boost::mpl::eval_if< boost::fusion::traits::is_sequence < type_t > , serialize_sequence < type_t > ,
typename boost::mpl::eval_if< is_container < type_t > , boost::mpl::identity < serialize_container < type_t > >,
serialize_pod < type_t > > >
::type type;
};
//
template <typename type_t>
struct simple_serializer : public resolve_serializer_type<type_t>::type { };
struct StructB
{
int s;
std::vector<int> vi_b;
};
struct StructA
{
int v;
std::vector<int> vi;
std::vector<StructB> lb;
};
BOOST_FUSION_ADAPT_STRUCT( StructB, (int , s) (std::vector<int>, vi_b) )
BOOST_FUSION_ADAPT_STRUCT( StructA, (int, v) (std::vector<int>, vi) (std::vector<StructB>, lb ) )
int main(int argc, char *argv[])
{
StructA sa_in;
std::string json_data = "{\"v\":20,\"vi\":[123,456,123],\"lb\":[{\"s\":999,\"vi_b\":[909,808]},{\"s\":888,\"vi_b\":[707]},{\"s\":777,\"vi_b\":[606,505,404,303]}]}";
std::stringstream is(json_data);
boost::property_tree::ptree pt;
boost::property_tree::json_parser::read_json(is, pt);
simple_serializer<StructA>::read_json( pt , sa_in);
}
错误信息： 1>e:\fusiongarage\apr_25\source.cpp(122): 错误 C2664: 'serialize_sequence::read_json' : 无法将参数 1 从 'std::basic_string<_elem>' 转换为 'boost::property_tree ::ptree &' 1> 与 1> [ 1> 序列_t=结构B 1>] 1> 和 1> [ 1> _Elem=字符， 1> _Traits=std::char_traits, 1> _Ax=std::分配器 1>] 1> e:\fusiongarage\apr_25\source.cpp(46) : 请参阅正在编译的函数模板实例化 'void serialize_container::read_json(boost::property_tree::ptree &,std::vector<_ty> &)' 的参考 1> 与 1> [ 1> container_type_t=std::vector, 1> _Ty=结构B 1>] 1> e:\fusiongarage\apr_25\source.cpp(44) : 编译类模板成员函数'void sequence_iterator::read_json(boost::property_tree::ptree &,sequence_t &)' 1> 与 1> [ 1> 序列_t=结构A， 1> index_t=boost::mpl::int_ 1>] 1> e:\fusiongarage\apr_25\source.cpp(48) : 参见正在编译的类模板实例化 'sequence_iterator' 的引用 1> 与 1> [ 1> 序列_t=结构A， 1> index_t=boost::mpl::int_ 1>] 1> 1>构建失败。
【问题讨论】：
标签： c++ json serialization