<optional>
Defines the container class template optional and several supporting templates.
Requirements
Header: <optional>
Namespace: std
Members
Operators
| Name | Description |
|---|---|
| operator== | Tests if an object is equal to another object. |
| operator!= | Tests if an object is not equal to another object. |
| operator< | Tests if the object on the left is less than the object on the right. |
| operator<= | Tests if the object on the left is less than or equal to the object on the right. |
| operator> | Tests if the object on the left is greater than the object on the right. |
| operator>= | Tests if the object on the left is greater than or equal to the object on the right. |
Note
In addition to relational compares, <optional> operators also support comparison with nullopt and T.
Functions
| Name | Description |
|---|---|
| make_optional | Makes an object optional. |
| swap | Swaps the contained values of two optional objects. |
Classes and Structs
| Name | Description |
|---|---|
| hash | Returns a hash of the contained object. |
| optional class | Describes an object that may or may not hold a value. |
| nullopt_t struct | Describes an object not holding a value. |
| bad_optional_access class | Describes an object thrown as an exception to report an attempt to access a value not there. |
Objects
| Name | Description |
|---|---|
| nullopt | An instance of nullopt_t for comparisons. |