nlohmann::basic_json::is_structured¶

constexpr bool is_structured() const noexcept;

This function returns true if and only if the JSON type is structured (array or object).

Return value¶

true if type is structured (array or object), 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_array() || is_object();
}

Notes¶

The term structured stems from RFC 8259:

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

Note that though strings are containers in C++, they are treated as primitive values in JSON.

Examples¶

Example

The following code exemplifies is_structured() 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_structured()
    std::cout << std::boolalpha;
    std::cout << j_null.is_structured() << '\n';
    std::cout << j_boolean.is_structured() << '\n';
    std::cout << j_number_integer.is_structured() << '\n';
    std::cout << j_number_unsigned_integer.is_structured() << '\n';
    std::cout << j_number_float.is_structured() << '\n';
    std::cout << j_object.is_structured() << '\n';
    std::cout << j_array.is_structured() << '\n';
    std::cout << j_string.is_structured() << '\n';
    std::cout << j_binary.is_structured() << '\n';
}

Output:

false
false
false
false
false
true
true
false
false

Version history¶

Added in version 1.0.0.

Last update: May 1, 2022