c++ - 因错误使用 CComPtr 对象而导致的编译错误

Question

我在我的类中定义了以下 CComPtr 对象和方法:

private:

    CComPtr<IRawPdu>& getRawPdu();
    // Returns the RawPdu interface pointer from the mRawPdu data member.
    // mRawPdu is initialized, if necessary.

    CComPtr<IRawPdu> mRawPdu;
    // Initialized to 0 in the ctor.  Uses lazy evaluation via getRawPdu().

在我的类的构造函数中，我通过初始化列表将 mRawPdu 初始化为 0。如果 mRawPdu 尚未初始化，则 getRawPdu() 方法使用惰性求值。

编译代码时出现如下错误:

Compiling...
topport.cpp
C:\Program Files\Microsoft Visual Studio 8\VC\atlmfc\include\atlcomcli.h(295) : error C2664: 'ATL::AtlComPtrAssign' : cannot convert parameter 2 from 'const ATL::CComPtr<T>' to 'IUnknown *'
        with
        [
            T=IRawPdu
        ]
        No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
        C:\Program Files\Microsoft Visual Studio 8\VC\atlmfc\include\atlcomcli.h(292) : while compiling class template member function 'IRawPdu *ATL::CComPtr<T>::operator =(const ATL::CComPtr<T> &) throw()'
        with
        [
            T=IRawPdu
        ]
        sessionutilities.h(186) : see reference to class template instantiation 'ATL::CComPtr<T>' being compiled
        with
        [
            T=IRawPdu
        ]
topglobals.cpp
C:\Program Files\Microsoft Visual Studio 8\VC\atlmfc\include\atlcomcli.h(295) : error C2664: 'ATL::AtlComPtrAssign' : cannot convert parameter 2 from 'const ATL::CComPtr<T>' to 'IUnknown *'
        with
        [
            T=IRawPdu
        ]
        No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
        C:\Program Files\Microsoft Visual Studio 8\VC\atlmfc\include\atlcomcli.h(292) : while compiling class template member function 'IRawPdu *ATL::CComPtr<T>::operator =(const ATL::CComPtr<T> &) throw()'
        with
        [
            T=IRawPdu
        ]
        sessionutilities.h(186) : see reference to class template instantiation 'ATL::CComPtr<T>' being compiled
        with
        [
            T=IRawPdu
        ]

对于可能导致此问题的原因有什么建议吗？

Answer 1

根据编译器给出的错误，它似乎无法推断出 IRawPdu 和 IUnknown 之间的转换。

它实际上是从 IUnknown 继承的吗？如果是这样，则可能是包含排序问题。您能否更深入地了解 IRawPdu 的层次结构