JSON for Modern C++  3.7.2

◆ type()

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 value_t nlohmann::basic_json::type ( ) const
inlineconstexprnoexcept

Return the type of the JSON value as a value from the value_t enumeration.

Returns
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
discarded value_t::discarded
Complexity
Constant.
Exception safety
No-throw guarantee: this member function never throws exceptions.
Example
The following code exemplifies type() 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()
19  std::cout << std::boolalpha;
20  std::cout << (j_null.type() == json::value_t::null) << '\n';
21  std::cout << (j_boolean.type() == json::value_t::boolean) << '\n';
22  std::cout << (j_number_integer.type() == json::value_t::number_integer) << '\n';
23  std::cout << (j_number_unsigned.type() == json::value_t::number_unsigned) << '\n';
24  std::cout << (j_number_float.type() == json::value_t::number_float) << '\n';
25  std::cout << (j_object.type() == json::value_t::object) << '\n';
26  std::cout << (j_array.type() == json::value_t::array) << '\n';
27  std::cout << (j_string.type() == json::value_t::string) << '\n';
28 }

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/type.cpp -o type 
See also
operator value_t() – return the type of the JSON value (implicit)
type_name() – return the type as string
Since
version 1.0.0

Definition at line 16614 of file json.hpp.

nlohmann::json
basic_json<> json
default JSON class
Definition: json.hpp:2445