Skip to content

# nlohmann::basic_json::is_primitive

    constexpr bool is_primitive() const noexcept;

This function returns `true` if and only if the JSON type is primitive (string, number, boolean, `null`, binary).

## Return value

`true` if type is primitive (string, number, boolean, `null`, or binary), `false` otherwise.

## Exception safety

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

## Complexity

Constant.

## Possible implementation

    constexpr bool is_primitive() const noexcept
    {
        return is_null() || is_string() || is_boolean() || is_number() || is_binary();
    }

## Notes

The term primitive stems from RFC 8259:

> JSON can represent four primitive types (strings, numbers, booleans, and null) and two structured types (objects and arrays).

This library extends primitive types to binary types, because binary types are roughly comparable to strings. Hence, `is_primitive()` returns `true` for binary values.

## Examples

Example

The following code exemplifies `is_primitive()` 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_float = 23.42;
        json j_number_unsigned_integer = 12345678987654321u;
        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_primitive()
        std::cout << std::boolalpha;
        std::cout << j_null.is_primitive() << '\n';
        std::cout << j_boolean.is_primitive() << '\n';
        std::cout << j_number_integer.is_primitive() << '\n';
        std::cout << j_number_unsigned_integer.is_primitive() << '\n';
        std::cout << j_number_float.is_primitive() << '\n';
        std::cout << j_object.is_primitive() << '\n';
        std::cout << j_array.is_primitive() << '\n';
        std::cout << j_string.is_primitive() << '\n';
        std::cout << j_binary.is_primitive() << '\n';
    }

Output:

    true
    true
    true
    true
    true
    false
    false
    true
    true

## See also

- is_structured() returns whether JSON value is structured
- is_null() returns whether JSON value is `null`
- is_string() returns whether JSON value is a string
- is_boolean() returns whether JSON value is a boolean
- is_number() returns whether JSON value is a number
- is_binary() returns whether JSON value is a binary array

## Version history

- Added in version 1.0.0.
- Extended to return `true` for binary types in version 3.8.0.

Last update: May 1, 2022
Back to top