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api/basic_json/is_structured/index.md

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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](https://tools.ietf.org/html/rfc8259):
+
+> 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()](https://json.nlohmann.me/api/basic_json/is_primitive/index.md) returns whether JSON value is primitive
+- [is_array()](https://json.nlohmann.me/api/basic_json/is_array/index.md) returns whether the value is an array
+- [is_object()](https://json.nlohmann.me/api/basic_json/is_object/index.md) returns whether the value is an object
+
+## Version history
+
+- Added in version 1.0.0.