json - 提升 read_json 和 C++11

Question

我正在尝试使用 Boost 的 property_tree 解析器和 C++11 代码来解析 JSON(我的系统是带有 gcc 4.7.2 和 Boost 1.49 的 Debian Wheezy)。我基于 Serializing and deserializing json with boost 尝试了以下代码:

#include <map>
#include <sstream>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
using boost::property_tree::ptree; using boost::property_tree::read_json; using    boost::property_tree::write_json;

void example() {
  // Write json.
  ptree pt;
  pt.put ("foo", "bar");
  std::ostringstream buf; 
  write_json (buf, pt, false);
  std::string json = buf.str(); // {"foo":"bar"}

  // Read json.
  ptree pt2;
  std::istringstream is (json);
  read_json (is, pt2);
  std::string foo = pt2.get<std::string> ("foo");
}

如果我用 g++ -std=c++03 -c' everything is fine. However, I also want to use C++11 features (which the code in the linked thread actually does!). But with 编译它g++ -std=c++11 -c' 我得到编译错误:

In file included from /usr/include/boost/property_tree/json_parser.hpp:14:0,
                 from test.cpp:4:
/usr/include/boost/property_tree/detail/json_parser_read.hpp: In instantiation of ‘void boost::property_tree::json_parser::context<Ptree>::a_literal_val::operator()   (boost::property_tree::json_parser::context<Ptree>::It,       boost::property_tree::json_parser::context<Ptree>::It) const [with Ptree = boost::property_tree::basic_ptree<std::basic_string<char>, std::basic_string<char> >; boost::property_tree::json_parser::context<Ptree>::It = __gnu_cxx::__normal_iterator<char*, std::vector<char, std::allocator<char> > >]’:
/usr/include/boost/spirit/home/classic/core/scanner/scanner.hpp:148:13:   required from ‘static void boost::spirit::classic::attributed_action_policy<boost::spirit::classic::nil_t>::call(const ActorT&, boost::spirit::classic::nil_t, const IteratorT&, const IteratorT&) [with ActorT = boost::property_tree::json_parser::context<boost::property_tree::basic_ptree<std::basic_string<char>, std::basic_string<char> > >::a_literal_val; IteratorT = __gnu_cxx::__normal_iterator<char*, std::vector<char, std::allocator<char> > >]’
/usr/include/boost/spirit/home/classic/core/scanner/scanner.hpp:163:13:   required from ‘void boost::spirit::classic::action_policy::do_action(const ActorT&, AttrT&, const IteratorT&, const IteratorT&) const [with ActorT = boost::property_tree::json_parser::context<boost::property_tree::basic_ptree<std::basic_string<char>, std::basic_string<char> > >::a_literal_val; AttrT = boost::spirit::classic::nil_t; IteratorT = __gnu_cxx::__normal_iterator<char*, std::vector<char, std::allocator<char> > >]’
...
test.cpp:20:1:   required from here
/usr/include/boost/property_tree/detail/json_parser_read.hpp:105:17: error: no matching function for call to ‘boost::property_tree::basic_ptree<std::basic_string<char>, std::basic_string<char> >::push_back(std::pair<std::basic_string<char>, std::basic_string<char> >)’
/usr/include/boost/property_tree/detail/json_parser_read.hpp:105:17: note: candidate is:
In file included from /usr/include/boost/property_tree/ptree.hpp:516:0,
             from test.cpp:3:
/usr/include/boost/property_tree/detail/ptree_implementation.hpp:362:9: note: boost::property_tree::basic_ptree<Key, Data, KeyCompare>::iterator boost::property_tree::basic_ptree<Key, Data, KeyCompare>::push_back(const value_type&) [with Key = std::basic_string<char>; Data = std::basic_string<char>; KeyCompare = std::less<std::basic_string<char> >; boost::property_tree::basic_ptree<Key, Data, KeyCompare>::value_type = std::pair<const std::basic_string<char>, boost::property_tree::basic_ptree<std::basic_string<char>, std::basic_string<char> > >]
/usr/include/boost/property_tree/detail/ptree_implementation.hpp:362:9: note:   no known conversion for argument 1 from ‘std::pair<std::basic_string<char>, std::basic_string<char> >’ to ‘const value_type& {aka const std::pair<const std::basic_string<char>, boost::property_tree::basic_ptree<std::basic_string<char>, std::basic_string<char> > >&}’

如何在 C++11 中使用 Boost 的 read_json？我是否需要更新的 Boost 版本(即从源代码手动安装，而不是使用 Wheezy 的打包版本)？我的代码有问题吗？或者这根本不可能？

Answer 1

这是一个 known bug较旧的 Boost 版本。
您可以通过应用以下补丁来修复它:

--- json_parser_read.hpp        2013-09-01 03:55:57.000000000 +0400
+++ /usr/include/boost/property_tree/detail/json_parser_read.hpp        2013-09-01 03:56:21.000000000 +0400
@@ -102,7 +102,7 @@
             void operator()(It b, It e) const
             {
                 BOOST_ASSERT(c.stack.size() >= 1);
-                c.stack.back()->push_back(std::make_pair(c.name, Str(b, e)));
+                c.stack.back()->push_back(std::make_pair(c.name, Ptree(Str(b, e))));
                 c.name.clear();
                 c.string.clear();
             }

或与

sed -i -e 's/std::make_pair(c.name, Str(b, e))/std::make_pair(c.name, Ptree(Str(b, e)))/' json_parser_read.hpp