Default Pointer Types

Pointers are not required to have an explicit attribute description. When an explicit attribute is not provided, the MIDL Compiler uses a default pointer attribute.

The default cases for unattributed pointers are the following:

• Top-level pointers that appear in parameter lists default to [ref] pointers.
• All other pointers default to the type specified by the [pointer_default] attribute. When no [pointer_default] attribute is supplied, these pointers default to the [ unique ] attribute when the MIDL compiler is in Microsoft Extensions mode or the [ptr] attribute when the MIDL compiler is in DCE-compatible mode.

When a remote procedure returns a pointer, the return value must be a [ unique ] or full ([ ptr ]) pointer.

/* IDL file compiled without /osf */
[ 
  uuid(ba209999-0c6c-11d2-97cf-00c04f8eea45),
  version(1.0),
  pointer_default(ptr)
]
interface MyInterface
{
    typedef long *PLONG;
  
    struct MyCircularList {
        struct MyCircularList *pRight;
        struct MyCircularList *pLeft;
        long Data;
    };

    void Foo1( [in] PLONG p );                   // p is ref
 
    void Foo2( [in] struct MyCircularList *p );  // p is ref, p->pRight and p->pLeft is ptr

    struct MyCircularList *Foo3( void );         // returned pointer is ptr.    
}

[ 
  uuid(ba209999-0c6c-11d2-97cf-00c04f8eea46),
  version(1.0)
]
interface MyInterface2
{
    struct MySingleList
       {
       struct MySingleList *pNext;
       long Data;
       };
    void Foo4( [in] struct MySingleList *p );  // p is ref, p->pNext is unique

    struct MySingleList *Foo5( void );         // returned pointer is unique.    
}

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

It is recommended that [ptr] is used only when pointer aliasing is required.