# is_structured - JSON for Modern C++
Author: Niels Lohmann

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# 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_structured() 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

## See also

- is_primitive() returns whether JSON value is primitive
- is_array() returns whether the value is an array
- is_object() returns whether the value is an object

## Version history

- Added in version 1.0.0.

November 12, 2025