c++11 - How to create and parse hierarchical/nested JSON with Poco C++? -


edited simplify , show exact code.

i have following data need serialize json parse json.

string name; std::map<string, string> metadata;

i need json nested/hierarchical this:

{     "name":"john smith"     "metadata":     {         "age":45,         "middle_name":"william",     }, }

here exact code:

void deserializefromjson(string &jsonstring) {     // parse json     poco::json::parser jsonparser;     poco::dynamic::var parsedjson = jsonparser.parse(jsonstring);     poco::dynamic::var parsedresult = jsonparser.result();      // extract json object     poco::dynamicstruct jsonstruct = *parsedresult.extract<poco::json::object::ptr>();      // name     name = jsonstruct["name"].tostring();      // meta data -- of these should use???     poco::dynamic::var metavar = jsonstruct["metadata"];     poco::json::object metaobj = jsonstruct["metadata"];      // @ point, have in 'metavar' , 'metaobj'?      // if try loop say, compiler error c2664 in "var.h"     (poco::json::object::constiterator itr = jsonobject.begin(), end = jsonobject.end(); itr != end; ++itr)     {         string metaname = itr->first;         string metavalue = itr->second.tostring();     } }

update: while putting example, found a subtle bug; fixed in repo upcoming 1.6.1 , 1.7.0 release. sample below works fine earlier releases, don't use preserve order json::stringifier::stringify() (using object::stringify() fine).

here go; if don't care preserving json entries insertion order, don't pass object constructor - perform better:

#include "poco/json/parser.h" #include "poco/json/parsehandler.h" #include "poco/json/stringifier.h"  using poco::json::parsehandler; using poco::json::stringifier; using poco::json::object; using poco::json::parser; using poco::dynamic::var; using poco::dynamicstruct;  void objprint(object& obj, const std::string& name = "") {     (object::constiterator = obj.begin(),         end = obj.end(); != end; ++it)     {         if (!name.empty()) std::cout << name << ':';         std::cout << it->first << ':';         if (it->second.type() == typeid(object::ptr))         {             object::ptr p = it->second.extract<object::ptr>();             objprint(*p, it->first);         }         else              std::cout << it->second.tostring() << std::endl;     } }  int main(int, char**) {     typedef std::map<std::string, int> personmap;      std::string timestamp = "2015-05-14t17:47:21.999z";     poco::int32 identifier = 3;     std::string name = "john smith";     personmap metadata;     metadata.insert(personmap::value_type("william", 45));      object obj(true);     obj.set("ts", timestamp);     obj.set("name", name);     obj.set("identifier", identifier);     object::ptr pmd = new poco::json::object(true);     (personmap::iterator = metadata.begin(),         end = metadata.end(); != end; ++it)     {         pmd->set("middle_name", it->first);         pmd->set("age", it->second);     }     obj.set("metadata", pmd);      std::ostringstream os;     obj.stringify(os, 2);     std::cout << os.str() << std::endl;      parser parser;     var result = parser.parse(os.str());      object::ptr pobj = result.extract<object::ptr>();     objprint(*pobj);      return 0; }

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