Unique Pointers

Unique pointers can change in value, but as with reference pointers, they do not cause aliasing of data — that is, the data that is accessible through the pointer is not accessible through any other name in the remote operation. This constraint saves a significant amount of processing.

The pointer itself can change from a null to a non-null value or from a non-null to a null value during the call. In the following example, the pointer is null before the call and points to a valid string after the call:

By default, the unique pointer attribute is applied to all pointers that are not parameters. In Microsoft-extensions mode, this default setting can be changed with the pointer_default attribute.

A unique pointer has the following characteristics:

• It can have the value NULL.
• It can change from null to non-null during the call. When the value changes to non-null, new memory is allocated on return.
• It can change from non-null to null during the call. When the value changes to NULL, the application is responsible for freeing the memory.
• If the value changes from one non-null value to another non-null value, the change is ignored.
• The storage that a unique pointer points to cannot be accessed by any other pointer or name in the operation.
• Return data is written into existing storage if the pointer does not have the value NULL.