Default Pointer Types for Pointers

The MIDL compiler offers three different default cases for pointers that do not have pointer attributes at definition time:

• Function parameters that are top-level pointers default to ref pointers.
• Pointers embedded in structures and pointers to other pointers (non-top-level pointers) default to the type specified by the pointer_default attribute.
• When no pointer_default attribute is supplied, non-top-level pointers default to unique pointers in MIDL's default (Microsoft-extensions) mode, and to ptr in DCE-compatible mode.

A pointer returned by a function must be a unique or full pointer. The MIDL compiler reports an error if a function result is, either explicitly or by default, a reference pointer. The returned pointer always indicates new storage because there is not enough information for the stubs to determine whether there is existing storage in the caller address space for pointer-valued function results.

Functions that return a pointer value can specify a pointer attribute as a function attribute. If a pointer attribute is not present, the function return pointer uses the value provided by the pointer_default attribute.

Note  To ensure unambiguous pointer-attribute behavior, always use explicit pointer attributes when defining a pointer.