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 the JSON value is structured
• is_null() returns whether the JSON value is null
• is_string() returns whether the JSON value is a string
• is_boolean() returns whether the JSON value is a boolean
• is_number() returns whether the JSON value is a number
• is_binary() returns whether the 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.