staj_object_iterator.md

jsoncons::staj_object_iterator

#include <jsoncons/staj_iterator.hpp>

template<
    typename Key,
    typename T,
    typename CharT=char
    > class staj_object_iterator

A staj_object_iterator is an InputIterator that accesses the individual stream events from a staj_cursor and, provided that when it is constructed the current stream event has type begin_object, it returns the elements of the JSON object as items of type std::pair<string_type,T>. If when it is constructed the current stream event does not have type begin_object, it becomes equal to the default-constructed iterator.

Member types

Member type	Definition
char_type	CharT
key_type	Key
value_type	std::pair<Key,T>
difference_type	std::ptrdiff_t
pointer	value_type*
reference	value_type&
iterator_category	std::input_iterator_tag

Constructors

staj_object_iterator() noexcept;                            (1)

staj_object_iterator(basic_staj_cursor<char_type>& cursor); (2)

staj_object_iterator(basic_staj_cursor<char_type>& cursor,
    std::error_code& ec);                                   (3)

staj_object_iterator(const staj_object_iterator& iter);     (4)

(1) Constructs the end iterator

(2) Constructs a staj_object_iterator that refers to the first member of the object following the current stream event begin_object. If there is no such member, returns the end iterator. If a parsing error is encountered, throws a ser_error.

(3) Constructs a staj_object_iterator that refers to the first member of the object following the current stream event begin_object. If there is no such member, returns the end iterator. If a parsing error is encountered, returns the end iterator and sets ec.

(4) Copy constructor

Member functions

const key_value_type& operator*() const

const key_value_type* operator->() const

staj_object_iterator& operator++();
staj_object_iterator operator++(int); 
staj_object_iterator& increment(std::error_code& ec);

Advances the iterator to the next object member.

Non-member functions

template <typename Key, typename T, typename CharT>
staj_object_iterator<Key, T, CharT> begin(staj_object_iterator<Key, T, CharT> iter);   (1)

template <typename T, typename CharT>
staj_object_iterator<Key, T, CharT> end(staj_object_iterator<Key, T, CharT>) noexcept; (2)

template <typename Key,typename T,typename CharT>
bool operator==(const staj_object_iterator<Key, T, CharT>& a, 
    const staj_object_iterator<Key, T, CharT>& b)                                      (3)

template <typename Key,typename T,typename CharT>
bool operator!=(const staj_object_iterator<Key, T, CharT>& a,                          (4)
    const staj_object_iterator<Key, T, CharT>& b)

(1)-(2) For range-based for loop support.

(3)-(4) As required by LegacyInputIterator

Examples

Iterate over a JSON object, returning key-json value pairs

const std::string example = R"(
{
   "application": "hiking",
   "reputons": [
   {
       "rater": "HikingAsylum.array_example.com",
       "assertion": "advanced",
       "rated": "Marilyn C",
       "rating": 0.90
     }
   ]
}
)";

int main()
{
    json_string_cursor cursor(example);

    auto iter = staj_object_iterator<std::string,json>(cursor);

    for (const auto& kv : iter)
    {
        std::cout << kv.first << ":\n" << pretty_print(kv.second) << "\n";
    }
    std::cout << "\n\n";
}

Output:

application:
"hiking"
reputons:
[
    {
        "assertion": "advanced",
        "rated": "Marilyn C",
        "rater": "HikingAsylum.array_example.com",
        "rating": 0.90
    }
]