json陣列如下：

{"var_name":"var1","positions":[0.1,0.1,0.1,0.1,0.1,0.1]},;

程式碼：

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

std::stringstream str_stream(json_content);
boost::property_tree::ptree root;
boost::property_tree::read_json(str_stream, root); 
 // get_child得到陣列物件
boost::property_tree::ptree positions_array = root.get_child("positions"); 
boost::property_tree::ptree::iterator pos = positions_array.begin();
for(; pos != positions_array.end(); ++pos)
{
   double value = pos->second.get_value<double>();
   std::cout<<"value "<<job <<std::endl;
}