MAPI IUnknown::AddRef

4/8/2010

The AddRef method increments the reference count for an interface on an object. It should be called for every new copy of a pointer to an interface on a given object.

Syntax

ULONG AddRef(void);

Parameters

None.

Return Value

Returns an integer from 1 to n, representing the value of the new reference count. This information for diagnostic or testing purposes only because, in certain situations, the value may be unstable.

Remarks

Objects use a reference counting mechanism to ensure that the lifetime of the object includes the lifetime of references to it. You use AddRef to stabilize a copy of an interface pointer. AddRef can also be called when the life of a cloned pointer must extend beyond the lifetime of the original pointer. The cloned pointer must be released by calling MAPI IUnknown::Release.

Objects must be able to maintain (231)-1 outstanding pointer references. Therefore, the internal reference counter that AddRef maintains must be a 32-bit unsigned integer.

Call this function for every new copy of an interface pointer that you make. For example, if you are passing a copy of a pointer back from a function, you must call AddRef on that pointer. You must also call AddRef on a pointer before passing it as an in-out parameter to a function; the function calls MAPI IUnknown::Release before copying the out-value on top of it.

Requirements

See Also

Reference

IUnknown for MAPI
MAPI IUnknown::Release

Other Resources

Messaging