JSON for Modern C++  3.7.0

◆ type_name()

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer>
const char* nlohmann::basic_json::type_name ( ) const
inlinenoexcept

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.

Returns
a string representation of a the m_type member:
Value type return value
null "null"
boolean "boolean"
string "string"
number "number" (for all number types)
object "object"
array "array"
discarded "discarded"
Exception safety
No-throw guarantee: this function never throws exceptions.
Complexity
Constant.
Example
The following code exemplifies type_name() for all JSON types.
1 #include <iostream>
2 #include <nlohmann/json.hpp>
3 
4 using json = nlohmann::json;
5 
6 int main()
7 {
8  // create JSON values
9  json j_null;
10  json j_boolean = true;
11  json j_number_integer = -17;
12  json j_number_unsigned = 42u;
13  json j_number_float = 23.42;
14  json j_object = {{"one", 1}, {"two", 2}};
15  json j_array = {1, 2, 4, 8, 16};
16  json j_string = "Hello, world";
17 
18  // call type_name()
19  std::cout << j_null << " is a " << j_null.type_name() << '\n';
20  std::cout << j_boolean << " is a " << j_boolean.type_name() << '\n';
21  std::cout << j_number_integer << " is a " << j_number_integer.type_name() << '\n';
22  std::cout << j_number_unsigned << " is a " << j_number_unsigned.type_name() << '\n';
23  std::cout << j_number_float << " is a " << j_number_float.type_name() << '\n';
24  std::cout << j_object << " is an " << j_object.type_name() << '\n';
25  std::cout << j_array << " is an " << j_array.type_name() << '\n';
26  std::cout << j_string << " is a " << j_string.type_name() << '\n';
27 }
basic_json<> json
default JSON class
Definition: json.hpp:2355

Output (play with this example online):
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
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/type_name.cpp -o type_name 
See also
type() – return the type of the JSON value
operator value_t() – return the type of the JSON value (implicit)
Since
version 1.0.0, public since 2.1.0, const char* and noexcept since 3.0.0

Definition at line 20813 of file json.hpp.