nlohmann::basic_json::value_t¶
enum class value_t : std::uint8_t {
null,
object,
array,
string,
boolean,
number_integer,
number_unsigned,
number_float,
binary,
discarded
};
This enumeration collects the different JSON types. It is internally used to distinguish the stored values, and the functions is_null
, is_object
, is_array
, is_string
, is_boolean
, is_number
(with is_number_integer
, is_number_unsigned
, and is_number_float
), is_discarded
, is_binary
, is_primitive
, and is_structured
rely on it.
Notes¶
There are three enumeration entries (number_integer, number_unsigned, and number_float), because the library distinguishes these three types for numbers: number_unsigned_t
is used for unsigned integers, number_integer_t
is used for signed integers, and number_float_t
is used for floating-point numbers or to approximate integers which do not fit in the limits of their respective type.
Examples¶
Example
The following code how type()
queries the value_t
for all JSON types.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// create JSON values
json j_null;
json j_boolean = true;
json j_number_integer = -17;
json j_number_unsigned = 42u;
json j_number_float = 23.42;
json j_object = {{"one", 1}, {"two", 2}};
json j_array = {1, 2, 4, 8, 16};
json j_string = "Hello, world";
// call type()
std::cout << std::boolalpha;
std::cout << (j_null.type() == json::value_t::null) << '\n';
std::cout << (j_boolean.type() == json::value_t::boolean) << '\n';
std::cout << (j_number_integer.type() == json::value_t::number_integer) << '\n';
std::cout << (j_number_unsigned.type() == json::value_t::number_unsigned) << '\n';
std::cout << (j_number_float.type() == json::value_t::number_float) << '\n';
std::cout << (j_object.type() == json::value_t::object) << '\n';
std::cout << (j_array.type() == json::value_t::array) << '\n';
std::cout << (j_string.type() == json::value_t::string) << '\n';
}
Output:
true
true
true
true
true
true
true
true
Version history¶
- Added in version 1.0.0.
- Added unsigned integer type in version 2.0.0.
- Added binary type in version 3.8.0.