json/api/basic_json/is_structured/index.md

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.