Convert rapidjson array iterator to rapidjson::value - c++

Question

How do I convert a rapidjson array iterator to a rapidjson::value?
I do not want answers that focus on how to get the contents of a rapid json array, or how to iterate through it.
I am also very aware that I can access members through the iterator using the example in the rapidjson documentation itr->name, but that is not what I want either. That form of working with rapidjson arrays already appears on many stack overflow questions and the rapidjson docs, and has been covered.
I need to end up with a rapidjson::value when starting with a rapidjson array iterator.
If we have an std::vector<int> than we can assign
std::vector<int>::iterator itMyInt = myvector.begin();
const int & myInt = *itMyInt;
I would expect to be able to do the same thing with a rapidjson array iterator, but my compiler disagrees.
The reason I need a rapidjson::value is that I'd like to reuse the same parsing method to parse the json object when is an element of an array, as I would when parsing that object on its own and not in an array.
Let me demonstrate with my minimal example:
// Rapid JSON Includes
#include <rapidjson/Document.h>
#include <rapidjson/StringBuffer.h>
#include <rapidjson/writer.h>
// Standard Includes
#include <exception>
#include <string>
#include <sstream>
//--------------------------------------------------------------------------------------------------
// NOTE -This stub cannot change
void ParseCar(const rapidjson::Value & carJson)
{
}
//--------------------------------------------------------------------------------------------------
int main()
{
std::string json =
"{"
" \"cars\" : ["
" {"
" \"name\" : \"Fiat\","
" \"price\" : 19.95"
" },"
" {"
" \"name\" : \"FRS\","
" \"price\" : 19995.00"
" }]"
"}";
// Parse the JSON
rapidjson::Document document;
document.Parse(json.c_str());
if (document.HasParseError())
{
// Error - Failed to parse JSON
std::ostringstream msg;
msg << "There was an error parsing the JSON"
<< " Error Code: " << document.GetParseError()
<< " Error Offset: " << document.GetErrorOffset();
throw std::exception(msg.str().c_str());
}
// Cars array
if (!document.HasMember("cars") ||
!document["cars"].IsArray())
{
std::string msg("Expected \"cars\" JSON array");
throw std::exception(msg.c_str());
}
const rapidjson::Value & carsArrayJSON = document["cars"];
/* Doesn't compile - No GetArray method exists
for (auto & carJSON : carsArrayJSON.GetArray())
{
}
*/
for (rapidjson::Value::ConstMemberIterator itCarJSON = carsArrayJSON.MemberBegin(); itCarJSON != carsArrayJSON.MemberEnd(); ++itCarJSON)
{
// Error - const rapidjson::GenericMember<Encoding,Allocator>' to 'const rapidjson::Value
const rapidjson::Value & carJSON = *itCarJSON;
ParseCar(carJSON);
}
return 0;
}

Answer 1

MemberIterator iterates Members of an Object. ValueIterator iterates Values in an Array.
Also, I'm not sure why that loop had issues for you, this compiles for me:
std::string json =
"{"
" \"cars\" : ["
" {"
" \"name\" : \"Fiat\","
" \"price\" : 19.95"
" },"
" {"
" \"name\" : \"FRS\","
" \"price\" : 19995.00"
" }]"
"}";
Document doc;
doc.Parse(json.data());
Value const& cars = doc["cars"];
for (auto& car : cars.GetArray()) {
cout << "name: " << car["name"].GetString() << " "
<< "price: " << car["price"].GetFloat() << endl;
}
And returns:
name: Fiat price: 19.95
name: FRS price: 19995
As for applying your function in a loop:
for (Value& car : cars.GetArray()) {
ParseCar(car);
}
If you must use an iterator:
for (Value::ValueIterator car = cars.Begin(); car != cars.End(); ++car) {
ParseCar(*car);
}
Or with auto:
for (auto car = cars.Begin(); car != cars.End(); ++car) {
ParseCar(*car);
}

Answer 2

Note: this will only work in an array.
Recently, I faced a similar problem and I came out with a different approach.
First, I set up a pointer to the desired path like so:
int myIterator = 0;
string myString = "/Layer1/Layer2/" + to_string(myIterator);
Pointer p(myString.c_str());
I now have a pointer to a variable path in my JSON object that varies with myIterator.
Then, I just used a for loop in which I use the SetValueByPointer function to append the pointer's value to a JSON object.