ArcGIS Engine Developer Guide

C++ APPLICATION PROGRAMMING INTERFACE
The compiler expands this as follows:
typedef _com_ptr_t< _com_IIID > IFooPtr;
Once declared, it is simply a matter of declaring a variable as the type of the
interface and appending Ptr to the end of the interface. Below are some common
uses of this smart pointer that you will see in the numerous C++ samples.
// Get a CLSID GUID constant.
extern "C" const GUID __declspec(selectany) CLSID_Foo = \
{0x2f3b470c,0xb01f,0x11d3,{0x83,0x8e,0x00,0x00,0x00,0x00,0x00,0x00}};
// Declare Smart Pointers for IFoo, IBar, and IGak interfaces.
_COM_SMARTPTR_TYPEDEF(IFoo, __uuidof(IFoo));
_COM_SMARTPTR_TYPEDEF(IBar, __uuidof(IBar));
_COM_SMARTPTR_TYPEDEF(IGak, __uuidof(IGak));
HRESULT SomeClass::Do()
{
// Create Instance of Foo class and QueryInterface (QI) for IFoo interface.
IFooPtr ipFoo;
HRESULT hr = ipFoo.CreateInstance(CLSID_Foo);
if (FAILED(hr)) return hr;
If you have used smart pointers before, you
might have seen differences in the implementation
of the equality (“==”) operator for smart
pointer comparisons. The COM specification
states object identification is performed by
comparing the pointer values of IUnknown. The
smart pointers will perform necessary QI and
comparison when using the “==” operator.
// Call method on IFoo to get IBar.
IBarPtr ipBar;
hr = ipFoo->get_Bar(&ipBar);
if (FAILED(hr)) return hr;
// QI IBar interface for IGak interface.
IGakPtr ipGak(ipBar);
// Call method on IGak.
hr = ipGak->DoSomething();
if (FAILED(hr)) return hr;
// Explicitly call Release().
ipGak = 0;
ipBar = 0;
// Let destructor call IFoo's Release.
return S_OK;
}
When working with CComBSTR, use the text mapping L“” to declare constant
OLECHAR strings. To display a CComBSTR at the command line, use wcerr.
You will need to include iostream to use wcerr.
CComBSTR bsName(L"Matt");
std::wcerr