JSON for Modern C++ 2.1.1
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◆ is_null()

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 bool nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::is_null ( ) const
inlineconstexprnoexcept

This function returns true iff the JSON value is null.

Returns
true if type is null, false otherwise.
Complexity\n Constant.
Exception safety\n No-throw guarantee: this member function never throws
exceptions.
Example\n The following code exemplifies is_null() for all JSON
types.
1#include <json.hpp>
2
3using json = nlohmann::json;
4
5int main()
6{
7 // create JSON values
9 json j_boolean = true;
11 json j_number_unsigned_integer = 12345678987654321u;
12 json j_number_float = 23.42;
13 json j_object = {{"one", 1}, {"two", 2}};
14 json j_array = {1, 2, 4, 8, 16};
15 json j_string = "Hello, world";
16
17 // call is_null()
18 std::cout << std::boolalpha;
19 std::cout << j_null.is_null() << '\n';
20 std::cout << j_boolean.is_null() << '\n';
21 std::cout << j_number_integer.is_null() << '\n';
22 std::cout << j_number_unsigned_integer.is_null() << '\n';
23 std::cout << j_number_float.is_null() << '\n';
24 std::cout << j_object.is_null() << '\n';
25 std::cout << j_array.is_null() << '\n';
26 std::cout << j_string.is_null() << '\n';
27}
static basic_json array(std::initializer_list< basic_json > init=std::initializer_list< basic_json >())
explicitly create an array from an initializer list
Definition json.hpp:2165
constexpr bool is_null() const noexcept
return whether value is null
Definition json.hpp:2760
a class to store JSON values
Definition json.hpp:1040
basic_json<> json
default JSON class
Definition json.hpp:12369

Output (play with this example online):
true
false
false
false
false
false
false
false

The example code above can be translated with
g++ -std=c++11 -Isrc doc/examples/is_null.cpp -o is_null 
Since
version 1.0.0

Definition at line 2760 of file json.hpp.