staj_array_iterator.md

jsoncons::staj_array_iterator

template <class T>
using staj_array_iterator = basic_staj_array_iterator<char,T>;

Header

#include <jsoncons/staj_iterator.hpp>

A staj_array_iterator is an InputIterator that accesses the individual stream events from a staj_reader and, provided that when it is constructed the current stream event has type staj_event_type::begin_array, it retrieves the elements of the JSON array as items of type T. If when it is constructed the current stream event does not have type staj_event_type::begin_array, it becomes equal to the default-constructed iterator.

Member types

Member type	Definition
char_type	char
value_type	T
difference_type	std::ptrdiff_t
pointer	value_type*
reference	value_type&
iterator_category	std::input_iterator_tag

Constructors

staj_array_iterator() noexcept; // (1)

staj_array_iterator(basic_staj_reader<char_type>& reader); // (2)

staj_array_iterator(basic_staj_reader<char_type>& reader,
                    std::error_code& ec); // (3)

(1) Constructs the end iterator

(2) Constructs a staj_array_iterator that refers to the first element of the array following the current stream event begin_array. If there is no such element, returns the end iterator. If a parsing error is encountered, throws a parse_error.

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

Member functions

const T& operator*() const

const T* operator->() const

staj_array_iterator& operator++()
staj_array_iterator& increment(std::error_code& ec)
staj_array_iterator operator++(int) 

Advances the iterator to the next array element.

Non-member functions

template <class T>
bool operator==(const staj_array_iterator<T>& a, const staj_array_iterator<T>& b)

template <class T>
bool operator!=(const staj_array_iterator<T>& a, const staj_array_iterator<T>& b)

template <class T>
staj_array_iterator<T> begin(staj_array_iterator<T> iter) noexcept; // (1)

template <class T>
staj_array_iterator<T> end(const staj_array_iterator<T>&) noexcept; // (2)

(1) Returns iter unchanged

(2) Returns a default-constructed stax_array_iterator, which serves as an end iterator. The argument is ignored.

The begin and end non-member functions enable the use of stax_array_iterators with range-based for loops.

Examples

Iterate over a JSON array, returning json values

const std::string example = R"(
[ 
  { 
      "employeeNo" : "101",
      "name" : "Tommy Cochrane",
      "title" : "Supervisor"
  },
  { 
      "employeeNo" : "102",
      "name" : "Bill Skeleton",
      "title" : "Line manager"
  }
]
)";

int main()
{
    std::istringstream is(example);

    json_staj_reader reader(is);

    staj_array_iterator<json> it(reader);

    for (const auto& j : it)
    {
        std::cout << pretty_print(j) << "\n";
    }
    std::cout << "\n\n";
}

Output:

{
    "employeeNo": "101",
    "name": "Tommy Cochrane",
    "title": "Supervisor"
}
{
    "employeeNo": "102",
    "name": "Bill Skeleton",
    "title": "Line manager"
}

Iterate over the JSON array, returning employee values

struct employee
{
    std::string employeeNo;
    std::string name;
    std::string title;
};

namespace jsoncons
{
    template<class Json>
    struct json_type_traits<Json, employee>
    {
    template<class Json>
    struct json_type_traits<Json, employee>
    {
        static bool is(const Json& j) noexcept
        {
            return j.is_object() && j.contains("employeeNo") && j.contains("name") && j.contains("title");
        }
        static employee as(const Json& j)
        {
            employee val;
            val.employeeNo = j["employeeNo"].template as<std::string>();
            val.name = j["name"].template as<std::string>();
            val.title = j["title"].template as<std::string>();
            return val;
        }
        static Json to_json(const employee& val)
        {
            Json j;
            j["employeeNo"] = val.employeeNo;
            j["name"] = val.name;
            j["title"] = val.title;
            return j;
        }
    };
}
      
int main()
{
    std::istringstream is(example);

    json_staj_reader reader(is);

    staj_array_iterator<employee> it(reader);

    for (const auto& val : it)
    {
        std::cout << val.employeeNo << ", " << val.name << ", " << val.title << "\n";
    }
    std::cout << "\n\n";
}

Output:

101, Tommy Cochrane, Supervisor
102, Bill Skeleton, Line manager