at.md

jsoncons::basic_json::at

basic_json& at(const string_view_type& name); (1)

const basic_json& at(const string_view_type& name) const; (2)

const basic_json& at_or_null(const string_view_type& name) const; (3)

basic_json& at(std::size_t i); (4)

const basic_json& at(std::size_t i) const; (5)

(1)-(2) return a reference to the value with the specifed name in a basic_json object. If not an object, an exception of type std::domain_error is thrown. if the object does not have a member with the specified name, an exception of type std::out_of_range is thrown.

(3) returns a const reference to the value in a basic_json object if name matches the name of a member, otherwise returns a const reference to a null basic_json value. Throws std::domain_error if not an object or null value.

(4)-(5) return a reference to the element at index i in a basic_json array. If not an array, an exception of type std::domain_error is thrown. if the index is outside the bounds of the array, an exception of type std::out_of_range is thrown.

Examples

Return a value if available, a null if not

#include <jsoncons/json.hpp>

int main()
{
    json j(json_object_arg, {{"author","Evelyn Waugh"},{"title","Sword of Honour"}});

    std::cout << "(1) " << j.at_or_null("author").as<std::string>() << "\n";
    std::cout << "(2) " << j.at_or_null("title").as<std::string>() << "\n";
    std::cout << "(3) " << j.at_or_null("category").as<std::string>() << "\n";
}

Output:

(1) Evelyn Waugh
(2) Sword of Honour
(3) null