nlohmann::basic_json::type_name¶
const char* type_name() const noexcept;
Returns the type name as string to be used in error messages -- usually to indicate that a function was called on a wrong JSON type.
Return value¶
a string representation of the type (value_t):
| Value type | return value |
|---|---|
null | "null" |
| boolean | "boolean" |
| string | "string" |
| number (integer, unsigned integer, floating-point) | "number" |
| object | "object" |
| array | "array" |
| binary | "binary" |
| discarded | "discarded" |
Exception safety¶
No-throw guarantee: this member function never throws exceptions.
Complexity¶
Constant.
Examples¶
Example
The following code exemplifies type_name() 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_name()
std::cout << j_null << " is a " << j_null.type_name() << '\n';
std::cout << j_boolean << " is a " << j_boolean.type_name() << '\n';
std::cout << j_number_integer << " is a " << j_number_integer.type_name() << '\n';
std::cout << j_number_unsigned << " is a " << j_number_unsigned.type_name() << '\n';
std::cout << j_number_float << " is a " << j_number_float.type_name() << '\n';
std::cout << j_object << " is an " << j_object.type_name() << '\n';
std::cout << j_array << " is an " << j_array.type_name() << '\n';
std::cout << j_string << " is a " << j_string.type_name() << '\n';
}
Output:
null is a null
true is a boolean
-17 is a number
42 is a number
23.42 is a number
{"one":1,"two":2} is an object
[1,2,4,8,16] is an array
"Hello, world" is a string
Version history¶
- Added in version 1.0.0.
- Part of the public API version since 2.1.0.
- Changed return value to
const char*and addednoexceptin version 3.0.0. - Added support for binary type in version 3.8.0.
Last update: May 1, 2022