DllGetClassObject返回“没有这样的接口支持”而CoCreateInstance可以找到它成功 [英] DllGetClassObject return "No such interface supported" while CoCreateInstance can find it successful

问题描述

我想使用库sqlceoledb35.dll来处理没有注册的.sdf db文件。我知道这个dll是一个COM dll并在ADO中使用。

但是我无法获得目标接口，它返回错误没有这样的接口支持。

以下是代码：

  CoInitialize（nullptr）; 
 HMODULE hmod = CoLoadLibrary（（Lsqlceoledb35.dll），true）; 
 DllGetClassObject_t pDllGetClassObject =（DllGetClassObject_t）GetProcAddress（hmod，DllGetClassObject）; 
 HRESULT hr = NOERROR; 
 IDBInitialize * pIDBInitialize1 = NULL; 
 IDBInitialize * pIDBInitialize2 = NULL; 
 hr = pDllGetClassObject（CLSID_SQLSERVERCE_3_5，__uuidof（IUnknown），（void **）& pIDBInitialize1）; 
 hr = pDllGetClassObject（CLSID_SQLSERVERCE_3_5，IID_IDBInitialize，（void **）& pIDBInitialize2）; 
  

但在此代码片段中， _uuidof（IUnknow）可以返回一个接口成功，但 IID_IDBInitialize 将失败（此IID可以在 CoCreateInstance 中工作， 。

这是另一个代码，可以在同一台机器上使用相同的接口IID正常工作：

  CoInitialize（nullptr）; 
 hr = CoCreateInstance（CLSID_SQLSERVERCE_3_5，
 0，
 CLSCTX_INPROC_SERVER，
 IID_IDBInitialize ，
（void **）& pIDBInitialize）; 
  

第一个代码片段可以工作？

那么方法 CoCreateInstance 做更多的工作，这是一个关键吗？

< divClass =h2_lin>解决方案

CoCreateInstance （对于in-proc服务器）分两个阶段工作：首先，加载DLL和调用 DllGetClassObject 与 CLSID 传递，要求 IClassFactory 。其次，它对这样获得的指针调用 IClassFactory :: CreateInstance ，并传递 IID 。

DllGetClassObject 知道如何创建的对象 - 类工厂 - 不通常本身实现任何 IClassFactory 以外的接口，当然还有 IUnknown 。

I want to use the library "sqlceoledb35.dll" to process .sdf db file without register. I know this dll is a COM dll and used in ADO.
But I can't get the target interface, it returns error "No such interface supported".
Here is the code:

    CoInitialize(nullptr); 
    HMODULE hmod = CoLoadLibrary((L"sqlceoledb35.dll"), true);
    DllGetClassObject_t pDllGetClassObject =(DllGetClassObject_t)GetProcAddress(hmod,        "DllGetClassObject");
    HRESULT hr=NOERROR;
    IDBInitialize *pIDBInitialize1=NULL;
    IDBInitialize *pIDBInitialize2=NULL;
    hr = pDllGetClassObject(CLSID_SQLSERVERCE_3_5, __uuidof(IUnknown), (void**)&pIDBInitialize1);
    hr = pDllGetClassObject(CLSID_SQLSERVERCE_3_5, IID_IDBInitialize, (void**)&pIDBInitialize2);

But in this code snippet, _uuidof(IUnknow)can return a interface success, but IID_IDBInitialize will fail(this IID can work in CoCreateInstance, you will see later.

This is another code which can work correctly in the same machine with the same interface IID:

    CoInitialize(nullptr); 
    hr = CoCreateInstance(  CLSID_SQLSERVERCE_3_5, 
                        0, 
                        CLSCTX_INPROC_SERVER, 
                        IID_IDBInitialize, 
                        (void**)&pIDBInitialize);

So anyone can help, So that the 1st code snippet can work?
So did the method CoCreateInstance do more work which is a key?

解决方案

CoCreateInstance (for in-proc servers) works in two stages. First, it loads the DLL and calls DllGetClassObject with the CLSID you pass, asking for IClassFactory interface. Second, it calls IClassFactory::CreateInstance on the pointer thus obtained, with the IID you pass.

The object that DllGetClassObject knows how to create - the class factory - does not normally itself implement any interfaces other than IClassFactory and, of course, IUnknown.

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