COM

inside declareinterface.h
...
static const GUID IID_IArmProperties = 
{ 0x1b8eb07c, 0xcb4b, 0x4118, { 0xbd, 0x61, 0x54, 0xb8, 0x77, 0x30, 0xb8, 0x55 } };

DECLARE_INTERFACE_(IArmProperties, IUnknown)
{
...
	STDMETHOD(DoSomething)(THIS_ CString csComment, THIS_ double *pdRetDbl, THIS_ MISCPARAM* mmpParam) PURE;
};

inside implement.h
#include "declareinterface.h"
...
class ATL_NO_VTABLE CArmPropertiesImp:
	public IArmProperties
{
public:
	CArmPropertiesImp(void);
	virtual ~CArmPropertiesImp(void);

	BEGIN_COM_MAP(CArmPropertiesImp)
		COM_INTERFACE_ENTRY(IArmProperties)
	END_COM_MAP()
...
	STDMETHOD(DoSomething)(CString csComment,double *pdRetDbl,MISCPARAM* mmpParam);
};

where:
typedef struct _MISCPARAM 
{
	double dObject; 
	LPCWSTR lpszObject;	
	long* plRes;
} MISCPARAM;			


inside implement.cpp
...
STDMETHODIMP CArmPropertiesImp::DoSomething(CString csComment,double *pdRetDbl,MISCPARAM* mmpParam)
{
	m_memberdouble+=mmpParam->dObject;
	//remember like in c, csComment is copied and passed by value to here 
	m_membercstring+=csComment;
	if(m_membercstring.IsEmpty())
		*pdRetDbl=m_memberdouble+0.5;
	else
		*pdRetDbl=m_memberdouble+1.5;

	return S_OK;
}

inside caller.cpp
...
	MISCPARAM locparam={0};
	locparam.dObject=1;

	CString cslocalComment="Test";
	double localdouble=0;

	IArmProperties *piArm=NULL;
	if(m_pIMaster->QueryInterface(IID_IArmProperties,(LPVOID*)&piArm)==S_OK)
		if(piAlarm)
		{
			piArm->DoSomething(cslocalComments,&localdouble,&locparam);
		}

	if(localdouble==0)
		DoTheFunction();
	else if(localdouble<0)
		DoOtherFunction();
	else
		DoSomeOtherFunction();
...