get.md

jsoncons::jsonpointer::get

Selects a json value.

Header

#include <jsoncons_ext/jsonpointer/jsonpointer.hpp>

template<class J>
std::tuple<J,jsonpointer_errc> get(const J& root, typename J::string_view_type path);

Return value

On success, returns the selected J value and a value-initialized jsonpointer_errc.

On error, returns a null J value and a jsonpointer_errc error code

Requirements

The type J satisfies the requirements for jsonpointer::get if it defines the following types

name	type	notes
value_type	J::value_type
reference	J::reference
const_reference	J::const_reference
pointer	J::pointer
const_pointer	J::const_pointer
string_type	J::string_type
string_view_type	J::string_view_type

and given

• a value index of type size_t
• a value key of type string_view_type
• an rvalue expression j of type J

the following expressions are valid

expression	return type	effects
is_array()	bool
is_object()	bool
size()	size_t
has_key(key)	bool
at(index)	reference or value_type
at(key)	reference or value_type

Examples

Examples from RFC6901

#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpointer/jsonpointer.hpp>

using namespace jsoncons;

int main()
{
    json example = json::parse(R"(
        {
          "foo": ["bar", "baz"],
          "": 0,
          "a/b": 1,
          "c%d": 2,
          "e^f": 3,
          "g|h": 4,
          "i\\j": 5,
          "k\"l": 6,
          " ": 7,
          "m~n": 8
       }
    )");
   
    json result;
    jsonpointer::jsonpointer_errc ec;

    std::tie(result,ec) = jsonpointer::get(example, "");
    std::cout << "(1) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/foo");
    std::cout << "(2) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/foo/0");
    std::cout << "(3) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/");
    std::cout << "(4) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/a~1b");
    std::cout << "(5) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/c%d");
    std::cout << "(6) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/e^f");
    std::cout << "(7) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/g|h");
    std::cout << "(8) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/i\\j");
    std::cout << "(9) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/k\"l");
    std::cout << "(10) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/ ");
    std::cout << "(11) " << result << std::endl;
    std::tie(result,ec) = jsonpointer::get(example, "/m~0n");
    std::cout << "(12) " << result << std::endl;
}

Output:

(1) {"":0," ":7,"a/b":1,"c%d":2,"e^f":3,"foo":["bar","baz"],"g|h":4,"i\\j":5,"k\"l":6,"m~n":8}
(2) ["bar","baz"]
(3) "bar"
(4) 0
(5) 1
(6) 2
(7) 3
(8) 4
(9) 5
(10) 6
(11) 7
(12) 8

Select author from second book

#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpointer/jsonpointer.hpp>

using namespace jsoncons;

int main()
{
    json root = json::parse(R"(
        [
          { "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
          },
          { "category": "fiction",
            "author": "Evelyn Waugh",
            "title": "Sword of Honour",
            "price": 12.99
          }
        ]
    )");

    json result;
    jsonpointer::jsonpointer_errc ec;
    std::tie(result,ec) = jsonpointer::get(root, "/1/author");

    if (ec == jsonpointer::jsonpointer_errc())
    {
        std::cout << result << std::endl;
    }
    else
    {
        std::cout << make_error_code(ec).message() << std::endl;
    }
}

Output:

"Evelyn Waugh"

Select values from cbor_view object

A cbor_view satisfies the requirements for jsonpointer::get.

#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpointer/jsonpointer.hpp>
#include <jsoncons_ext/cbor/cbor.hpp>

using namespace jsoncons;

int main()
{
    ojson j1 = ojson::parse(R"(
    {
       "application": "hiking",
       "reputons": [
       {
           "rater": "HikingAsylum.example.com",
           "assertion": "is-good",
           "rated": "sk",
           "rating": 0.90
         }
       ]
    }
    )");

    auto buffer = cbor::encode_cbor(j1);

    cbor::cbor_view b1(buffer); 

    cbor::cbor_view b2;
    jsonpointer::jsonpointer_errc ec;

    std::tie(b2,ec) = jsonpointer::get(b1,"/reputons/0/rated");

    ojson j2 = cbor::decode_cbor<ojson>(b2);

    std::cout << j2 << std::endl;
}

Output:

"sk"