JSON for Modern C++  3.7.0

◆ operator value_t()

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>
constexpr nlohmann::basic_json::operator value_t ( ) const
inlinenoexcept

Implicitly return the type of the JSON value as a value from the value_t enumeration.

Returns
the type of the JSON value
Complexity
Constant.
Exception safety
No-throw guarantee: this member function never throws exceptions.
Example
The following code exemplifies the value_t operator 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 operator value_t()
19  json::value_t t_null = j_null;
20  json::value_t t_boolean = j_boolean;
21  json::value_t t_number_integer = j_number_integer;
22  json::value_t t_number_unsigned = j_number_unsigned;
23  json::value_t t_number_float = j_number_float;
24  json::value_t t_object = j_object;
25  json::value_t t_array = j_array;
26  json::value_t t_string = j_string;
27 
28  // print types
29  std::cout << std::boolalpha;
30  std::cout << (t_null == json::value_t::null) << '\n';
31  std::cout << (t_boolean == json::value_t::boolean) << '\n';
32  std::cout << (t_number_integer == json::value_t::number_integer) << '\n';
33  std::cout << (t_number_unsigned == json::value_t::number_unsigned) << '\n';
34  std::cout << (t_number_float == json::value_t::number_float) << '\n';
35  std::cout << (t_object == json::value_t::object) << '\n';
36  std::cout << (t_array == json::value_t::array) << '\n';
37  std::cout << (t_string == json::value_t::string) << '\n';
38 }
basic_json<> json
default JSON class
Definition: json.hpp:2355
detail::value_t value_t
Definition: json.hpp:14614

Output (play with this example online):
true
true
true
true
true
true
true
true
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/operator__value_t.cpp -o operator__value_t 
See also
type() – return the type of the JSON value (explicit)
type_name() – return the type as string
Since
version 1.0.0

Definition at line 16763 of file json.hpp.