nlohmann::basic_json::operator value_t¶
constexpr operator value_t() const noexcept;
Return the type of the JSON value as a value from the value_t
enumeration.
Return value¶
the type of the JSON value
Value type | return value |
---|---|
null | value_t::null |
boolean | value_t::boolean |
string | value_t::string |
number (integer) | value_t::number_integer |
number (unsigned integer) | value_t::number_unsigned |
number (floating-point) | value_t::number_float |
object | value_t::object |
array | value_t::array |
binary | value_t::binary |
discarded | value_t::discarded |
Exception safety¶
No-throw guarantee: this member function never throws exceptions.
Complexity¶
Constant.
Examples¶
Example
The following code exemplifies operator 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 operator value_t()
json::value_t t_null = j_null;
json::value_t t_boolean = j_boolean;
json::value_t t_number_integer = j_number_integer;
json::value_t t_number_unsigned = j_number_unsigned;
json::value_t t_number_float = j_number_float;
json::value_t t_object = j_object;
json::value_t t_array = j_array;
json::value_t t_string = j_string;
// print types
std::cout << std::boolalpha;
std::cout << (t_null == json::value_t::null) << '\n';
std::cout << (t_boolean == json::value_t::boolean) << '\n';
std::cout << (t_number_integer == json::value_t::number_integer) << '\n';
std::cout << (t_number_unsigned == json::value_t::number_unsigned) << '\n';
std::cout << (t_number_float == json::value_t::number_float) << '\n';
std::cout << (t_object == json::value_t::object) << '\n';
std::cout << (t_array == json::value_t::array) << '\n';
std::cout << (t_string == 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.
Last update: May 1, 2022