BEGIN_COM_MAP

「爱情、让人受尽委屈。」 2021-11-17 01:44 312阅读 0赞

1，offsetofclass  
获取基类相对于子类的偏移位置。  
  
\#define \_ATL\_PACKING 8  
\#define offsetofclass(base, derived) ((DWORD\_PTR)(static\_cast<base\*>((derived\*)\_ATL\_PACKING))-\_ATL\_PACKING)  
  
\_ATL\_PACKING非零就行，只是作为一个地址。因为为了避免虚类无法创建对象的问题所以没有通过类对象来计算。  
  
![aHR0cHM6Ly9pbWFnZXMyMDE1LmNuYmxvZ3MuY29tL2Jsb2cvNDg3NDc5LzIwMTYwOS80ODc0NzktMjAxNjA5MDYxOTE0MTIwMDQtMjgzNjc4MTA5LnBuZw][]  
  
2，  
//If you get a message that FinalConstruct is ambiguous then you need to  
// override it in your class and call each base class' version of this  
\#define BEGIN\_COM\_MAP(x) public: \\  
    typedef x \_ComMapClass; \\  
    IUnknown\* \_GetRawUnknown() throw() \\  
    **\{ ATLASSERT(\_GetEntries()\[0\].pFunc == \_ATL\_SIMPLEMAPENTRY); return (IUnknown\*)((INT\_PTR)this+\_GetEntries()->dw); \}**** **\\  
    \_ATL\_DECLARE\_GET\_UNKNOWN(x)\\  
    HRESULT \_InternalQueryInterface(REFIID iid, void\*\* ppvObject) throw() \\  
    \{ return InternalQueryInterface(this, \_GetEntries(), iid, ppvObject); \} \\  
    const static ATL::\_ATL\_INTMAP\_ENTRY\* WINAPI \_GetEntries() throw() \{ \\  
    **static const ATL::\_ATL\_INTMAP\_ENTRY \_entries\[\] **= \{ DEBUG\_QI\_ENTRY(x)  
  
  
**struct \_ATL\_INTMAP\_ENTRY  
\{  
    const IID\* piid; // the interface id (IID)  
    DWORD\_PTR dw;  
    \_ATL\_CREATORARGFUNC\* pFunc; //NULL:end, 1:offset, n:ptr  
\};**  
  
\#define DEBUG\_QI\_ENTRY(x) \\  
        \{NULL, \\  
        (DWORD\_PTR)\_T(\#x), \\  
        (ATL::\_ATL\_CREATORARGFUNC\*)0\},  
  
typedef HRESULT (WINAPI \_ATL\_CREATORARGFUNC)(void\* pv, REFIID riid, LPVOID\* ppv, DWORD\_PTR dw);  
  
  
\#define COM\_INTERFACE\_ENTRY(x)\\  
    \{&\_ATL\_IIDOF(x), \\  
    offsetofclass(x, \_ComMapClass), \\  
    **\_ATL\_SIMPLEMAPENTRY**\},  
  
\#define \_ATL\_IIDOF(x) \_\_uuidof(x)  
//\_\_uuidof获取与x相关的GUID值  
  
**\#define \_ATL\_SIMPLEMAPENTRY ((ATL::\_ATL\_CREATORARGFUNC\*)1)**  
  
\#define END\_COM\_MAP() \\  
    \_\_if\_exists(\_GetAttrEntries) \{ \{NULL, (DWORD\_PTR)\_GetAttrEntries, \_ChainAttr \}, \}\\  
    \{NULL, 0, 0\}\}; return &\_entries\[1\];\} \\  
    virtual ULONG STDMETHODCALLTYPE AddRef( void) throw() = 0; \\  
    virtual ULONG STDMETHODCALLTYPE Release( void) throw() = 0; \\  
    STDMETHOD(QueryInterface)(REFIID, void\*\*) throw() = 0;  
  
3，  
static HRESULT WINAPI CComObjectRootBase ::InternalQueryInterface(void\* pThis,  
        const \_ATL\_INTMAP\_ENTRY\* pEntries, REFIID iid, void\*\* ppvObject)  
    \{  
        ATLASSERT(pEntries->pFunc == \_ATL\_SIMPLEMAPENTRY);  
        HRESULT hRes = AtlInternalQueryInterface(pThis, pEntries, iid, ppvObject);  
        return \_ATLDUMPIID(iid, pszClassName, hRes);  
    \}  
  
  
// QI support  
ATLINLINE ATLAPI AtlInternalQueryInterface(  
    \_Inout\_ void\* pThis,  
    \_In\_ const \_ATL\_INTMAP\_ENTRY\* pEntries,  
    \_In\_ REFIID iid,  
    \_COM\_Outptr\_ void\*\* ppvObject)  
\{  
    // First entry in the com map should be a simple map entry  
    ATLASSERT(pEntries->pFunc == \_ATL\_SIMPLEMAPENTRY);  
  
    if (InlineIsEqualUnknown(iid)) // use first interface  
    \{  
        IUnknown\* pUnk = (IUnknown\*)((INT\_PTR)pThis+pEntries->dw);  
        pUnk->AddRef();  
        \*ppvObject = pUnk;  
        return S\_OK;  
    \}  
  
    HRESULT hRes;  
    for (;; pEntries++)  
    \{  
        if (pEntries->pFunc == NULL)  
        \{  
            hRes = E\_NOINTERFACE;  
            break;  
        \}  
  
        BOOL bBlind = (pEntries->piid == NULL);  
        if (bBlind || InlineIsEqualGUID(\*(pEntries->piid), iid))  
        \{  
            if (pEntries->pFunc == \_ATL\_SIMPLEMAPENTRY) //offset  
            \{  
                ATLASSERT(!bBlind);  
                IUnknown\* pUnk = (IUnknown\*)((INT\_PTR)pThis+pEntries->dw);  
                pUnk->AddRef();  
                \*ppvObject = pUnk;  
                return S\_OK;  
            \}  
  
            // Actual function call   
            hRes = pEntries->pFunc(pThis,  
                iid, ppvObject, pEntries->dw);  
            if (hRes == S\_OK)  
                return S\_OK;  
            if (!bBlind && FAILED(hRes))  
                break;  
        \}  
    \}  
  
    \*ppvObject = NULL;  
    return hRes;  
\}  
CComObjectRootBase的InternalQueryInterface内部调用AtlInternalQueryInterface遍历\_ATL\_INTMAP\_ENTRY数组（包含所有实现接口的映射表），找到基类的虚函数表返回。  
（我原来用的VS2005,没有AtlInternalQueryInterface的实现，蛋疼了好久这个接口映射表的怎么返回的，我猜也是遍历但是没有看见源码一直心头惴惴不安。后面擦查看VS2013里面给出了AtlInternalQueryInterface的实现才把这口气舒出来。）  
  
4，  
ATL提供了BEGIN\_COM\_MAP、END\_COM\_MAP、COM\_INTERFACE\_ENTRY与COM\_INTERFACE\_ENTRY2这4个宏来创建接口映射表。  
假设一个类CClassA继承了接口IIntA1和IIntA2，则该类的接口映射表创建如下：  
  
class CClassA : public CComObjectRootEx<CComSingleThreadMode>  
\{  
    BEGIN\_COM\_MAP(CClassA)  
        COM\_INTERFACE\_ENTRY(IIntA1)  
        COM\_INTERFACE\_ENTRY(IIntA2)  
    END\_COM\_MAP()  
    ......  
\};  
  
static const ATL::\_ATL\_INTMAP\_ENTRY \_entries\[\] =  
\{  
\{NULL,     (DWORD\_PTR)\_T(\#x),     (ATL::\_ATL\_CREATORARGFUNC\*)0\},  
\{& \_\_uuidof(IIntA1), offsetofclass(IIntA1, CClassA), (ATL::\_ATL\_CREATORARGFUNC\*)1\},  
\{& \_\_uuidof(IIntA2), offsetofclass(IIntA2, CClassA), (ATL::\_ATL\_CREATORARGFUNC\*)1\},  
\{NULL, 0, 0\}  
\};  
![aHR0cHM6Ly9pbWFnZXMyMDE1LmNuYmxvZ3MuY29tL2Jsb2cvNDg3NDc5LzIwMTYwOS80ODc0NzktMjAxNjA5MDYxOTE0MTI1MzUtMTg2MTcxOTUyMC5wbmc][]  
  
  
而当CClassB继承了IIntB1和IIntB2，并且IIntB1和IIntB2都继承自IDispatch接口。  
此时，如果客户程序在查询IDispatch接口，QueryInterface所返回的IDispatch接口指针将无法确定其属于IIntB1还是IIntB2。  
在这种情况下，需要指定IDispatch接口指针的默认指向。 COM\_INTERFACE\_ENTRY2()宏即是用于完成该功能。  
下面代码将对IDispatch接口的请求默认指向属于IIntB2的IDispatch接口指针。  
class CClassB : public CComObjectRootEx<CComSingleThreadMode>  
\{  
    BEGIN\_COM\_MAP(CClassB)  
        COM\_INTERFACE\_ENTRY(IIntB1)  
        COM\_INTERFACE\_ENTRY(IIntB2)  
        COM\_INTERFACE\_ENTRY2(IDispatch, IIntB2)  
    END\_COM\_MAP()  
    ......  
\};

\#define COM\_INTERFACE\_ENTRY2(x, x2)\\  
    \{&\_ATL\_IIDOF(x),\\  
    reinterpret\_cast<DWORD\_PTR>(static\_cast<x\*>(static\_cast<x2\*>(reinterpret\_cast<\_ComMapClass\*>(8))))-8,\\  
    \_ATL\_SIMPLEMAPENTRY\},  
  
5，总结：  
BEGIN\_COM\_MAP通过一个静态的\_GetEntries()方法，来获取在该方法中创建的一个静态COM接口映射表。

原文：[https://www.cnblogs.com/liuhan333/p/5843313.html][https_www.cnblogs.com_liuhan333_p_5843313.html]

[aHR0cHM6Ly9pbWFnZXMyMDE1LmNuYmxvZ3MuY29tL2Jsb2cvNDg3NDc5LzIwMTYwOS80ODc0NzktMjAxNjA5MDYxOTE0MTIwMDQtMjgzNjc4MTA5LnBuZw]: /images/20211116/f121483e43e94a8f84749875658ed32b.png
[aHR0cHM6Ly9pbWFnZXMyMDE1LmNuYmxvZ3MuY29tL2Jsb2cvNDg3NDc5LzIwMTYwOS80ODc0NzktMjAxNjA5MDYxOTE0MTI1MzUtMTg2MTcxOTUyMC5wbmc]: /images/20211116/8da22149f0b644b9836b045d552b74de.png
[https_www.cnblogs.com_liuhan333_p_5843313.html]: https://www.cnblogs.com/liuhan333/p/5843313.html

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