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 = int64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator>

bool nlohmann::basic_json::is_null ( ) const

inlinenoexcept

This function returns true iff the JSON value is null.

Returns

true if value type is null, false otherwise.

Complexity

Constant.

Example

The following code exemplifies is_null for all JSON value types.

#include <json.hpp>

using namespace nlohmann;

int main()
{
    // create JSON values
    json j_null;
    json j_boolean = true;
    json j_number_integer = 17;
    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 is_null()
    std::cout << std::boolalpha;
    std::cout << j_null.is_null() << '\n';
    std::cout << j_boolean.is_null() << '\n';
    std::cout << j_number_integer.is_null() << '\n';
    std::cout << j_number_float.is_null() << '\n';
    std::cout << j_object.is_null() << '\n';
    std::cout << j_array.is_null() << '\n';
    std::cout << j_string.is_null() << '\n';
}

Output:

true
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 

.