[DirectShow][DECLARE_IUNKNOWN]_see declaration of 'cmy333view-优快云博客

本文链接：https://blog.youkuaiyun.com/flight_lcf/article/details/1351673

本文介绍了在DirectShow中创建自定义Filter时遇到的问题及解决方法。若自定义接口继承了IUnknown，需要在实现中添加DECLARE_IUNKNOWN宏，否则会因未实现纯虚函数而无法实例化。

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　　最近在学习编写Filter，如果新增加一个接口的话并继承于IUnknown的话，首要在自定义接口的实现中添加DECLARE_IUNKNOWN宏．否则会有如下的提示．

C:/DirectShowStudy/Filter/ＭyFilter.cpp(41) : error C2259: 'CＭyFilter' : cannot instantiate abstract class due to following members:
        C:/DirectShowStudy/Filter4/ＭyFilter.h(16) : see declaration of 'CＭyFilter
C:/DirectShowStudy/Filter4/ＭyFilter.cpp(41) : warning C4259: 'long __stdcall IUnknown::QueryInterface(const struct _GUID &,void ** )' : pure virtual function was not defined
        D:/Program Files/Microsoft Visual Studio/VC98/INCLUDE/unknwn.h(109) : see declaration of 'QueryInterface'
C:/DirectShowStudy/Filter4ＭyFilter.cpp(41) : warning C4259: 'unsigned long __stdcall IUnknown::AddRef(void)' : pure virtual function was not defined
        D:/Program Files/Microsoft Visual Studio/VC98/INCLUDE/unknwn.h(113) : see declaration of 'AddRef'
C:/DirectShowStudy/Filter4/ＭyFilter.cpp(41) : warning C4259: 'unsigned long __stdcall IUnknown::Release(void)' : pure virtual function was not defined
        D:/Program Files/Microsoft Visual Studio/VC98/INCLUDE/unknwn.h(115) : see declaration of 'Release'

代码举例说明：　

//IMyTitle.h

DECLARE_INTERFACE_(IMyTitle, IUnknown)
{
STDMETHOD(GetTitleCount) (THIS_
long *inType
) PURE;
};

//'CＭyFilter

class CＭyFilter : public CTransInPlaceFilter

,public IMyTitle

{

public:

DECLARE_IUNKNOWN;

};