COM Interface Entry Points
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For member functions of a COM interface, use the METHOD_PROLOGUE macro to maintain the proper global state when calling methods of an exported interface.
Typically, member functions of interfaces implemented by CCmdTarget-derived objects already use this macro to provide automatic initialization of the pThis pointer. For example:
STDMETHODIMP_(ULONG) CMySink::XSinky::AddRef()
{
METHOD_PROLOGUE(CMySink, Sinky);
return pThis->InternalAddRef();
}
For additional information, see Technical Note 38 on MFC/OLE IUnknown implementation.
The METHOD_PROLOGUE macro is defined as:
#define METHOD_PROLOGUE(theClass, localClass) \
theClass* pThis = \
((theClass*)((BYTE*)this - offsetof(theClass, m_x##localClass))); \
AFX_MANAGE_STATE(pThis->m_pModuleState) \
The portion of the macro concerned with managing the global state is:
AFX_MANAGE_STATE( pThis->m_pModuleState )
In this expression, m_pModuleState is assumed to be a member variable of the containing object. It is implemented by the CCmdTarget base class and is initialized to the appropriate value by COleObjectFactory, when the object is instantiated.