c++ - Boost Variant: How to model JSON? -

i'm trying parse json string using boost spirit store json object recursive data structures:

value <== [null, bool, long, double, std::string, array, object]; array <== [value, value, value, ...]; object <== ["name1": value, "name2": value, ...]; 

and here's code:

#include <map> #include <vector> #include <string> #include <boost/variant.hpp> #include <boost/shared_array.hpp> #include <boost/shared_ptr.hpp>  struct jsonnull {}; struct jsonvalue;  typedef std::map<std::string, jsonvalue *> jsonobject; typedef std::vector<jsonvalue *> jsonarray;  struct jsonvalue : boost::variant<jsonnull, bool, long, double, std::string, jsonarray, jsonobject> { };  jsonvalue aval = jsonobject(); 

when compiling error:

error c2440: 'initializing' : cannot convert 'std::map<_kty,_ty>' 'jsonvalue' 

moreover, how safely cast jsonvalue jsonobject? when try doing:

boost::get<jsonobject>(aval) = jsonobject(); 

this gets run-time exception/fatal failure.

any appreciated.

edit:

following @nicol's advice, came out following code:

struct jsonnull {}; struct jsonvalue;  typedef std::map<std::string, jsonvalue *> jsonobject; typedef std::vector<jsonvalue *> jsonarray; typedef boost::variant<     jsonnull, bool, long, double, std::string,     jsonobject, jsonarray,     boost::recursive_wrapper<jsonvalue> > jsondatavalue;  struct jsonvalue {     jsondatavalue data; }; 

i can work on jsonobject & jsonarray easy this:

jsonvalue *pjsonval = new jsonvalue();  boost::get<jsonobject>(pcurrval->data).insert(     std::pair<std::string, jsonvalue *>("key", pjsonval) );  boost::get<jsonarray>(pcurrval->data).push_back(pjsonval); 

just posting benefit this.

you have use recursive wrapper (and shouldn't deriving boost::variant):

struct jsonvalue;  typedef boost::variant</*types*/, boost::recursive_wrapper<jsonvalue> > jsondatavalue;  struct jsonvalue {     jsondatavalue value; }; 

to make boost.spirit take jsonvalue, need write 1 of fusion adaptor things adapt raw variant type struct.

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moreover, how safely cast jsonvalue jsonobject? when try doing:

that's not how variants work. if want set them value, set them other value:

jsonvalue val; val.value = jsonvalue();