提升read_json和write_json对于属性树不是等价的

Question

If I create a property tree from a stringstream with read_json, and I write it back to the stream with write_json, tryng to load it again with read_json fails with "terminate called after throwing an instance of 'boost::exception_detail::clone_impl >' what(): (1): expected object or array"

This code fails with the forementioned exception:

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
using boost::property_tree::ptree;
ptree pt;
stringstream pippo("{\"size\":1000,\"reserved\":100,\"list\": {\"122\":1,\"123\":3}}");
read_json(pippo,pt);
write_json(pippo,pt,false);
read_json(pippo,pt);

BUT if I change my code this way, it works:

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
using boost::property_tree::ptree;
ptree pt;
stringstream pippo("{\"size\":1000,\"reserved\":100,\"list\": {\"122\":1,\"123\":3}}");
read_json(pippo,pt);
write_json(pippo,pt,false);
stringstream pluto(pippo.str());
read_json(pluto,pt);

Answer 1

I write down the answer just in case someone makes the same mistake I did.

read_json is designed for file, not string stream access, so when I feed it a stringstream written by from write_json, the stream was simply at eof. This code now works:

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
using boost::property_tree::ptree;
ptree pt;
stringstream pippo("{\"size\":1000,\"reserved\":100,\"list\": {\"122\":1,\"123\":3}}");
read_json(pippo,pt);
write_json(pippo,pt,false);
pippo.seekg(0,pippo.beg);
read_json(pippo,pt);