在END_COM_MAP中IUnknown成员函数的目的是什么？ [英] What's the purpose of IUnknown member functions in END_COM_MAP?

问题描述

ATL END_COM_MAP巨集的定义如下：

  #define END_COM_MAP（）\ 
 __if_exists（_GetAttrEntries） {{NULL，（DWORD_PTR）_GetAttrEntries，_ChainAttr}，} \ 
 {NULL，0，0}};返回_entries;} \ 
 virtual ULONG STDMETHODCALLTYPE AddRef（void）throw（）= 0; \ 
 virtual ULONG STDMETHODCALLTYPE Release（void）throw（）= 0; \ 
 STDMETHOD（QueryInterface）（REFIID，void **）throw（）= 0; 
  

它用于从COM接口继承的类的定义中，例如：

  class ATL_NO_VTABLE CMyClass：
 public CComCoClass< CMyClass，& MyClassGuid>，
 public CComObjectRoot，
 public IMyComInterface 
 {
 public：
 BEGIN_COM_MAP（CMyClass）
 COM_INTERFACE_ENTRY（IMyComInterface）
 END_COM_MAP（）
}; 
  

这意味着QueryInterface（），AddRef（）和Release类。因为我没有定义它们的实现，所以这个类应该是不可修改的。

它是如何工作的，为什么这些IUnknown成员函数在这里重新声明？ >解决方案

这是一段时间，因为我使用ATL但是，IIRC，什么结束了实例化不是 CMyClass ，但 CComObject< CMyClass> 。

CComObject implements IUnknown ，并继承其模板参数

编辑： ATL COM对象的基础页面上很好地说明了发生了什么。

ATL END_COM_MAP macro is defined as follows:

#define END_COM_MAP() \
    __if_exists(_GetAttrEntries) {{NULL, (DWORD_PTR)_GetAttrEntries, _ChainAttr }, }\
    {NULL, 0, 0}}; return _entries;} \
    virtual ULONG STDMETHODCALLTYPE AddRef( void) throw() = 0; \
    virtual ULONG STDMETHODCALLTYPE Release( void) throw() = 0; \
    STDMETHOD(QueryInterface)(REFIID, void**) throw() = 0;

It is intended to be used within definition of classes inherited from COM interfaces, for example:

class ATL_NO_VTABLE CMyClass :
    public CComCoClass<CMyClass, &MyClassGuid>,
    public CComObjectRoot,
    public IMyComInterface
{
public:
    BEGIN_COM_MAP( CMyClass )
        COM_INTERFACE_ENTRY( IMyComInterface)
    END_COM_MAP()
};

This means that QueryInterface(), AddRef() and Release() are declared as pure virtual in this class. Since I don't define their implementation this class should be uncreatable. Yet ATL successfully instantiates it.

How does it work and why are those IUnknown member functions redeclared here?

解决方案

It's been a while since I used ATL but, IIRC, what ends up being instantiated is not CMyClass, but CComObject<CMyClass>.

CComObject implements IUnknown and inherits from its template parameter.

Edit: The "Fundamentals of ATL COM Objects" page on MSDN nicely illustrates what's going on.

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