Skip to content

# 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.

Back to top