The following code fragment binds to the root of the global catalog (GC:) and enumerates the single object (which is the root of the forest) so that it can be used to search the entire forest.

Set gc = GetObject("GC:")
For each child in gc
    Set entpr = child
Next
' Now entpr is an object that can used
' to search the entire forest.

The following code fragment contains a function that returns an IDirectorySearch pointer that can be used to search the entire forest.

The function does a serverless bind to the root of GC:, enumerates the single item (which is the root of the forest and can be used to search the entire forest), calls QueryInterface to get an IDirectorySearch pointer to the object, and returns that pointer for use by the caller to search the forest.

HRESULT GetGC(IDirectorySearch **ppDS)
{
HRESULT hr;
IEnumVARIANT *pEnum = NULL;
IADsContainer *pCont = NULL;
VARIANT var;
IDispatch *pDisp = NULL;
ULONG lFetch;
 
// Set IDirectorySearch pointer to NULL.
*ppDS = NULL;
 
// First, bind to the GC: namespace container object. 
hr = ADsOpenObject(TEXT("GC:"),
                NULL,
                NULL,
                ADS_SECURE_AUTHENTICATION, //Use Secure Authentication
                IID_IADsContainer,
                (void**)&pCont);
if (FAILED(hr)) {
    _tprintf(TEXT("ADsOpenObject failed: 0x%x\n"), hr);
    goto cleanup;
} 
 
// Get an enumeration interface for the GC container to enumerate the 
// contents. The "real" GC is the only child of the GC container.
hr = ADsBuildEnumerator(pCont, &pEnum);
if (FAILED(hr)) {
    _tprintf(TEXT("ADsBuildEnumerator failed: 0x%x\n"), hr);
    goto cleanup;
} 
 
// Now enumerate. There's only one child of the GC: object.
hr = pEnum->Next(1, &var, &lFetch);
if (FAILED(hr)) {
    _tprintf(TEXT("ADsEnumerateNext failed: 0x%x\n"), hr);
    goto cleanup;
} 
 
// Get the IDirectorySearch pointer.
if (( hr == S_OK ) && ( lFetch == 1 ) )     
{    
    pDisp = V_DISPATCH(&var);
    hr = pDisp->QueryInterface( IID_IDirectorySearch, (void**)ppDS); 
}
 
cleanup:
 
if (pEnum)
    ADsFreeEnumerator(pEnum);
if (pCont)
    pCont->Release();
if (pDisp)
    (pDisp)->Release();
return hr;
}