COM in plain C, Part 4

// This is a C example that tests the IExample2 COM component (in IExample2.dll).

#include <windows.h>
#include <objbase.h>
#include <stdio.h>
#include "../IExample2/IExample2.h"

int main(int argc, char **argv)
{
	IExample2		*exampleObj;
	IClassFactory	*classFactory;
	HRESULT			hr;

	// We must initialize OLE before we do anything with COM objects. NOTE:
	// some COM components, such as the IE browser engine, require that you
	// use OleInitialize() instead. But our COM component doesn't require this
	if (!CoInitialize(0))
	{
		// Get IExample2.DLL's IClassFactory
		if ((hr = CoGetClassObject(&CLSID_IExample2, CLSCTX_INPROC_SERVER, 0, &IID_IClassFactory, &classFactory)))
			MessageBox(0, "Can't get IClassFactory", "CoGetClassObject error", MB_OK|MB_ICONEXCLAMATION);
		else
		{
			// Create an IExample object
			if ((hr = classFactory->lpVtbl->CreateInstance(classFactory, 0, &IID_IExample2, &exampleObj)))
			{
				classFactory->lpVtbl->Release(classFactory);
				MessageBox(0, "Can't create IExample object", "CreateInstance error", MB_OK|MB_ICONEXCLAMATION);
			}
			else
			{
				BSTR	str;

				// Release the IClassFactory. We don't need it now that we have the one
				// IExample we want
				classFactory->lpVtbl->Release(classFactory);

				// Alloc a BSTR and call SetString to set the text "Hello world!"
				if (!(str = SysAllocString(L"Hello world!")))
					MessageBox(0, "Can't create BSTR", "SysAllocString error",  MB_OK|MB_ICONEXCLAMATION);

				else
				{
					exampleObj->lpVtbl->SetString(exampleObj, str);

					// Free the BSTR above
					SysFreeString(str);

					// Retrieve the string to make sure we get "Hello world!"
					if (exampleObj->lpVtbl->GetString(exampleObj, &str))
						MessageBox(0, "GetString failed", "GetString error",  MB_OK|MB_ICONEXCLAMATION);
					else
					{
						MessageBoxW(0, str, L"GetString return", MB_OK);

						// Free the BSTR that GetString allocated for us
						SysFreeString(str);
					}
				}

				// Release the IExample now that we're done with it
				exampleObj->lpVtbl->Release(exampleObj);
			}
		}

		// When finally done with OLE, free it
		CoUninitialize();
	}
	else
		MessageBox(0, "Can't initialize COM", "CoInitialize error", MB_OK|MB_ICONEXCLAMATION);

	return(0);
}