Enumerator Example

OLE DB Programmer's Reference

The code in this example shows how to create and use an enumerator object.

///////////////////////////////////////////////////////////////// // myCreateEnumerator // // This function creates an enumerator, obtains a sources rowset // from it, displays the rowset to the user, and allows the user // to specify the ProgID of a provider. The CLSID that matches // this ProgID is retuned to the caller in *pCLSID. // ///////////////////////////////////////////////////////////////// HRESULT myCreateEnumerator    (    REFCLSID             clsidEnumerator,    CLSID *              pCLSID    ) {    HRESULT              hr;    IUnknown *           pIUnkEnumerator               = NULL;    ISourcesRowset *     pISourcesRowset               = NULL;    IRowset *            pIRowset                      = NULL;    IDBInitialize *      pIDBInitialize                = NULL;    WCHAR                wszProgID[MAX_NAME_LEN + 1]   = {0};        const ULONG          cProperties                   = 2;    DBPROP               rgProperties[cProperties];    DBPROPSET            rgPropSets[1];    // Create the enumerator object. We ask for IUnknown when creating    // the enumerator because some enumerators may require initialization    // before we can obtain a sources rowset from the enumerator. This is    // indicated by whether or not the enumerator object exposes    // IDBInitialize. (We don't want to ask for IDBInitialize, since    // enumerators that don't require initialization will cause the    // CoCreateInstance to fail.)    XCHECK_HR(hr = CoCreateInstance(             clsidEnumerator,            // clsid--enumerator             NULL,                       // pUnkOuter             CLSCTX_INPROC_SERVER,       // dwClsContext             IID_IUnknown,               // riid             (void**)&pIUnkEnumerator));  // ppvObj                 // If the enumerator exposes IDBInitialize, we need to initialize it.    if( SUCCEEDED(hr = pIUnkEnumerator->QueryInterface(IID_IDBInitialize,       (void**)&pIDBInitialize)) )    {       CHECK_HR(hr = myDoInitialization(pIUnkEnumerator));    }    // Set properties on the rowset, to request additional functionality.    myAddRowsetProperties(rgPropSets, cProperties, rgProperties);    // Obtain a sources rowset from the enumerator. This rowset contains    // all of the OLE DB providers that this enumerator is able to list.    XCHECK_HR(hr = pIUnkEnumerator->QueryInterface(IID_ISourcesRowset,              (void**)&pISourcesRowset));    XCHECK_HR(hr = pISourcesRowset->GetSourcesRowset(              NULL,                    // pUnkOuter              IID_IRowset,             // riid              1,                       // cPropSets              rgPropSets,              // rgPropSets              (IUnknown**)&pIRowset));  // ppRowset          // Display the rowset to the user. This will allow the user to    // perform basic navigation of the rowset and will allow the user    // to select a row containing a desired provider.    CHECK_HR(hr = myDisplayRowset(pIRowset,             L"SOURCES_NAME", MAX_NAME_LEN, wszProgID));    // Obtain the ProgID for the provider to use from the user.    // The default value for this is the value of the SOURCES_NAME    // column in the row selected by the user previously.    myGetInputFromUser(wszProgID, L"\nType the ProgID of a provider"                       L" to use [Enter = `%s`]: ", wszProgID);    XCHECK_HR(hr = CLSIDFromProgID(wszProgID, pCLSID)); CLEANUP:    if( pIUnkEnumerator )       pIUnkEnumerator->Release();    if( pISourcesRowset )       pISourcesRowset->Release();    if( pIRowset )       pIRowset->Release();    if( pIDBInitialize )       pIDBInitialize->Release();    return hr; }

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