json/api/basic_json/is_structured.md

nlohmann::basic_json::is_structured

constexpr bool is_structured() const noexcept;

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

Return value

#!cpp true if type is structured (array or object), #!cpp 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.

```cpp
#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:

```json
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.