c++boostjsoncppboost-iteratorsiterator-facade

Using JsonCPP ValueIterator with STL algorithms


I know, ValueIterator from JsonCPP cannot be used in standard STL algorithms directly. But is there a some "indirect" way to use it in STL algorithms (maybe via Boost.Iterator or something like this)? I want something likes to following:

Json::Value root = getJson(); //came from outside
std::vector<Json::Value> vec;

std::copy
  ( make_some_smart_iterator(...) // some iterator produced with start of root
  , make_some_smart_iterator(...) // some iterator produced with end of root
  , std::back_inserter(vec)
  );

Solution

  • There is a custom iterator derived from boost::iterator_facade.

    #include <boost/iterator/iterator_facade.hpp>
    
    class JsonIter : public boost::iterator_facade
         <JsonIter, Json::ValueIterator, boost::forward_traversal_tag, Json::Value &>
    {
    public:
        JsonIter() {}
        explicit JsonIter(Json::ValueIterator iter) : m_iter(iter) {}
    private:
        friend class boost::iterator_core_access;
    
        void increment() { ++m_iter; }
        bool equal(const JsonIter &other) const {return this->m_iter == other.m_iter;}
        Json::Value &dereference() const { return *m_iter; }
        Json::ValueIterator m_iter;
    };
    

    And client code is following:

    std::copy(JsonIter(root.begin()), JsonIter(root.end()), std::back_inserter(vec));