错误C2664：无法从'const ATL :: CAdapt <atl :: ccomptr <izipfileentry>＆gt;转换参数2 *'to'ATL :: CAdapt <atl :: ccomptr <izipfileentry>＆gt; *'</ATL ::但是CComPtr <izipfileentry> </ATL ::但是CComPtr <izipfileentry>

Question

我将VS2008（VC ++）代码迁移到VS2013。我收到以下错误：

error C2664: 'HRESULT _CopyItfFromAdaptItf<IZipFileEntry>::copy(T **,ATL::CAdapt<ATL::CComPtr<T>> *)' : cannot convert argument 2 from 'const ATL::CAdapt<ATL::CComPtr<IZipFileEntry>> *' to 'ATL::CAdapt<ATL::CComPtr<IZipFileEntry>> *'

错误出现在Visual Studio SDK文件中，怎么可能？我无法解决此错误。请在下面找到输出和错误行。

非常感谢您的帮助!!

输出：

C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\atlmfc\include\atlcom.h(5818): error C2664: 'HRESULT _CopyItfFromAdaptItf<IZipFileEntry>::copy(T **,ATL::CAdapt<ATL::CComPtr<T>> *)' : cannot convert argument 2 from 'const ATL::CAdapt<ATL::CComPtr<IZipFileEntry>> *' to 'ATL::CAdapt<ATL::CComPtr<IZipFileEntry>> *'
      with
      [
          T=IZipFileEntry
      ]
      Conversion loses qualifiers
      C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\atlmfc\include\atlcom.h(5803) : while compiling class template member function 'HRESULT ATL::ICollectionOnSTLImpl<IZipFileDir1,EntryList,IZipFileEntry *,_CopyItfFromAdaptItf<IZipFileEntry>,EntryEnum>::get_Item(long,ItemType *)'
      with
      [
          ItemType=IZipFileEntry *
      ]
      C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\atlmfc\include\atlcom.h(5140) : see reference to class template instantiation 'ATL::ICollectionOnSTLImpl<IZipFileDir1,EntryList,IZipFileEntry *,_CopyItfFromAdaptItf<IZipFileEntry>,EntryEnum>' being compiled

错误代码：

if (iter != m_coll.end())
      hr = CopyItem::copy(pvar, &*iter); // Error C2664
return hr;

P.S：我无法编辑和保存此atlcom.h文件。我得到访问路径被拒绝的错误消息。这是因为它是一个SDK文件吗？

添加了更多代码定义：

struct _CopyItfFromAdaptItf {
    static HRESULT copy(T** p1, CAdapt< CComPtr<T> >* p2) {
    if( *p1 = p2->m_T ) return (*p1)->AddRef(), S_OK;
    return E_POINTER;
}


IZipFileEntry : public IDispatch
{
    public:
        virtual /* [helpstring][id][propget] */ HRESULT STDMETHODCALLTYPE get_name( 
        /* [retval][out] */ BSTR *pVal) = 0;

        virtual /* [helpstring][id][propget] */ HRESULT STDMETHODCALLTYPE get_lastModified( 
        /* [retval][out] */ DATE *pVal) = 0;

        virtual /* [helpstring][id][propget] */ HRESULT STDMETHODCALLTYPE get_fileSize( 
        /* [retval][out] */ long *pVal) = 0;

        virtual /* [helpstring][id][propget] */ HRESULT STDMETHODCALLTYPE get_compressedSize( 
        /* [retval][out] */ long *pVal) = 0;

    };


typedef ICollectionOnSTLImpl<IZipFileDir1, EntryList, IZipFileEntry*, _CopyItfFromAdaptItf<IZipFileEntry>, EntryEnum> EntryCollection;

ICollectionOnSTLImpl的定义

class ICollectionOnSTLImpl : 
    public T
{
public:
        STDMETHOD(get_Count)(_Out_ long* pcount)
        {
        if (pcount == NULL)
            return E_POINTER;
        ATLASSUME(m_coll.size()<=LONG_MAX);

        *pcount = (long)m_coll.size();

        return S_OK;
    }
    STDMETHOD(get_Item)(
        _In_ long Index, 
        _Out_ ItemType* pvar)
    {
        //Index is 1-based
        if (pvar == NULL)
            return E_POINTER;
        if (Index < 1)
            return E_INVALIDARG;
        HRESULT hr = E_FAIL;
        Index--;
        CollType::const_iterator iter = m_coll.begin();
        while (iter != m_coll.end() && Index > 0)
        {
            iter++;
            Index--;
        }
        if (iter != m_coll.end())
            hr = CopyItem::copy(pvar, &*iter);
        return hr;
    }
    STDMETHOD(get__NewEnum)(_Outptr_ IUnknown** ppUnk)
    {
        if (ppUnk == NULL)
            return E_POINTER;
        *ppUnk = NULL;
        HRESULT hRes = S_OK;
        CComObject<EnumType>* p;
        hRes = CComObject<EnumType>::CreateInstance(&p);
        if (SUCCEEDED(hRes))
        {
            hRes = p->Init(this, m_coll);
            if (hRes == S_OK)
                hRes = p->QueryInterface(__uuidof(IUnknown), (void**)ppUnk);
        }
        if (hRes != S_OK)
            delete p;
        return hRes;
    }
    CollType m_coll;
};

Answer 1

如果没有所有代码，很难肯定地说，但看起来我用以下代码重现了这个问题：

template<class T>
struct _CopyItfFromAdaptItf {
    static HRESULT copy(T** p1, CAdapt< CComPtr<T> >* p2) {
        if( *p1 = p2->m_T ) return (*p1)->AddRef(), S_OK;
        return E_POINTER;
    }
};

IDispatch** disp;
const CAdapt<CComPtr<IDispatch>> adapt; // note const here
_CopyItfFromAdaptItf<IDispatch>::copy( disp, &adapt ); //error C2664 here

编译器输出

File(Line) : error C2664: '_CopyItfFromAdaptItf<T>::copy' :
  cannot convert parameter 2 from 'const ATL::CAdapt<T> *' to 'ATL::CAdapt<T> *'
    with
    [
      T=IDispatch
    ]
    and
    [
      T=ATL::CComPtr<IDispatch>
    ]
    and
    [
      T=ATL::CComPtr<IDispatch>
    ]
    Conversion loses qualifiers

几乎与您引用的输出相匹配。

问题是_CopyItfFromAdaptItf::copy()想要一个指向非const的指针，但是传递了一个指向const的指针。传递指向const的指针的代码位于atlcom.h里面，它属于SDK头文件，因此你最好不要更改它。

此外，如果更改_CopyItfFromAdaptItf::copy()签名以接受指向const的指针：

static HRESULT copy(T** p1, const CAdapt< CComPtr<T> >* p2) // note addition of const

它仍然编译得很好。 _CopyItfFromAdaptItf在ATL标题中没有任何地方，所以我猜它在您的代码中，您可以更改它。

所以看起来解决方案就是简单地改变_CopyItfFromAdaptItf::copy()来接受指向const的指针，问题就会消失。