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nlohmann::basic_json::is_null

constexpr bool is_null() const noexcept;

This function returns true if and only if the JSON value is null.

Return value

true if type is null, false otherwise.

Exception safety

No-throw guarantee: this member function never throws exceptions.

Complexity

Constant.

Examples

Example

The following code exemplifies is_null() for all JSON types.

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    // create JSON values
    json j_null;
    json j_boolean = true;
    json j_number_integer = 17;
    json j_number_unsigned_integer = 12345678987654321u;
    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";
    json j_binary = json::binary({1, 2, 3});

    // 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_unsigned_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';
    std::cout << j_binary.is_null() << '\n';
}

Output:

true
false
false
false
false
false
false
false
false

Version history

  • Added in version 1.0.0.
Last update: May 1, 2022