实施dllRegisterserver方法

我正在尝试实现com的dllregisterserver方法。
所以我读了本教程：
http://www.codeguru.com/cpp/com-tech/activex/tutorials/article.php/c5567/step-by-step-com-tutorial.htm

我遵循这些步骤，直到dllregisterserver的部分。
这是他们的实施：

HRESULT  __stdcall DllRegisterServer(void)
    {
    //
    //As per COM guidelines, every self installable COM inprocess component
    //should export the function DllRegisterServer for printing the 
    //specified information to the registry
    //
    //
    WCHAR *lpwszClsid;
    char szBuff[MAX_PATH]="";
    char szClsid[MAX_PATH]="", szInproc[MAX_PATH]="",szProgId[MAX_PATH];
    char szDescriptionVal[256]="";
    StringFromCLSID(
            CLSID_AddObject,
            &lpwszClsid);
    wsprintf(szClsid,"%S",lpwszClsid);
    wsprintf(szInproc,"%s\%s\%s","clsid",szClsid,"InprocServer32");
    wsprintf(szProgId,"%s\%s\%s","clsid",szClsid,"ProgId");

    //
    //write the default value 
    //
    wsprintf(szBuff,"%s","Fast Addition Algorithm");
    wsprintf(szDescriptionVal,"%s\%s","clsid",szClsid);
    HelperWriteKey (
                HKEY_CLASSES_ROOT,
                szDescriptionVal,
                NULL,//write to the "default" value
                REG_SZ,
                (void*)szBuff,
                lstrlen(szBuff)
                );

    //
    //write the "InprocServer32" key data
    //
    GetModuleFileName(
                g_hModule,
                szBuff,
                sizeof(szBuff));
    HelperWriteKey (
                HKEY_CLASSES_ROOT,
                szInproc,
                NULL,//write to the "default" value
                REG_SZ,
                (void*)szBuff,
                lstrlen(szBuff)
                );
    //
    //write the "ProgId" key data under HKCRclsid{---}ProgId
    //
    lstrcpy(szBuff,AddObjProgId);
    HelperWriteKey (
                HKEY_CLASSES_ROOT,
                szProgId,
                NULL,
                REG_SZ,
                (void*)szBuff,
                lstrlen(szBuff)
                );

    //
    //write the "ProgId" data under HKCRCodeGuru.FastAddition
    //
    wsprintf(szBuff,"%s","Fast Addition Algorithm");
    HelperWriteKey (
                HKEY_CLASSES_ROOT,
                AddObjProgId,
                NULL,
                REG_SZ,
                (void*)szBuff,
                lstrlen(szBuff)
                );

    wsprintf(szProgId,"%s\%s",AddObjProgId,"CLSID");
    HelperWriteKey (
                HKEY_CLASSES_ROOT,
                szProgId,
                NULL,
                REG_SZ,
                (void*)szClsid,
                lstrlen(szClsid)
                );
    return 1;
    }

clsid_addobject被这样定义：

// {92E7A9C2-F4CB-11d4-825D-00104B3646C0}
static const GUID CLSID_AddObject = 
{ 0x92e7a9c2, 0xf4cb, 0x11d4, { 0x82, 0x5d, 0x0, 0x10, 0x4b, 0x36, 0x46, 0xc0 } };

我不明白的是： 1.为什么他们使用StringFromCLSID将GUID作为字符串获取？他们已经有了它，由于某种原因，他们将其转换为IID？我们在IDL文件中提供的GUID是否足够好？
2.需要注册哪些GUID？图书馆的指导？接口的指导？班级指南？或所有这些？