错误C2259：无法实例化抽象类

本文介绍了错误C2259：无法实例化抽象类的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ 我使用Visual Studio 2010创建一个ATL项目，并在此项目中添加一个ATL简单对象类。在构建过程中没有任何错误。但是当我声明一个类对象，比如 CCartoPoint pt 时，我收到错误消息错误C2259：'CCartoPoint'：无法实例化抽象类 在以下代码中，错误消息来自方法' STDMETHODIMP CCartoPoint :: get_Centroid（ICartoPoint ** pCentroidVal）'。 我已经检查了 .h 文件中的方法数量， .h 文件和 .cpp 文件相同。 * .IDL文件： [ object， uuid （14428BC6-A897- 4268 -8FFD-B4947DEDDFC6）， dual ，不可扩展， pointer_default（唯一）] interface ICartoPoint：IDispatch { [propget， id（ 2 ）] HRESULT X（[out，retval] DOUBLE * pVal）; [propput，id（ 2 ）] HRESULT X（[ in ] DOUBLE newVal）; [propget，id（ 3 ）] HRESULT Y（[out，retval] DOUBLE * pVal）; [propput，id（ 3 ）] HRESULT Y（[ in ] DOUBLE newVal）; }; [ object， uuid （238155D0-220A-4BFA-90D2-46E27461E314）， dual，不可扩展， pointer_default（唯一）] interface ICartoGeometry：IDispatch { [propget，id（ 1 ）] HRESULT区域（[out，retval] DOUBLE * pAreaVal）; [propget，id（ 2 ）] HRESULT Centroid（[out，retval] ICartoPoint ** pCentroidVal）; [propget，id（ 3 ）] HRESULT GeometryType（[out，retval] cartoGeometryType * pTypeVal）; // [propget，id（4）] HRESULT坐标（[out，retval] ICartoCoordinate ** pCdsVal ，[out] DOUBLE * pCountVal）; [propget，id（ 5 ）] HRESULT NumGeometries（[out，retval] LONG * pNumberVal ）; [propget，id（ 6 ）] HRESULT NumPoints（[out，retval] LONG * pNumberVal）; [propget，id（ 7 ）] HRESULT坐标（[out，retval] ICartoCoordinate ** pVal）; }; * .h文件 class ATL_NO_VTABLE CCartoPoint： public CComObjectRootEx< CComSingleThreadModel>， public CComCoClass< CCartoPoint，& CLSID_CartoPoint>， public IDispatchImpl< ICartoPoint，& IID_ICartoPoint，& LIBID_GeometryObjectLib ， / * wMajor = * / 1 ， / * wMinor = * / 0> ;, public IDispatchImpl< ICartoGeometry，& IID_ICartoGeometry，& LIBID_GeometryObjectLib， / * wMajor = * / 1 ， / * wMinor = * / 0> { public ： CCartoPoint（） { m_pCoordinate = 新坐标（ 0 ， 0 ）; GeometryFactory工厂; m_pPoint = factory.createPoint（* m_pCoordinate）; } CCartoPoint（DOUBLE x，DOUBLE y） { m_pCoordinate = new 坐标（x，y）; GeometryFactory工厂; m_pPoint = factory.createPoint（* m_pCoordinate）; } DECLARE_REGISTRY_RESOURCEID（IDR_CARTOPOINT） BEGIN_COM_MAP（CCartoPoint） COM_INTERFACE_ENTRY（ICartoPoint） COM_INTERFACE_ENTRY2 （IDispatch，ICartoPoint） COM_INTERFACE_ENTRY（ICartoGeometry） END_COM_MAP（） DECLARE_PROTECT_FINAL_CONSTRUCT（） HRESULT FinalConstruct（ ） { return S_OK; } void FinalRelease（） {} public ： STDMETHOD（get_X）（DOUBLE * pVal）; STDMETHOD（put_X）（DOUBLE newVal）; STDMETHOD（get_Y）（DOUBLE * pVal）; STDMETHOD（put_Y）（DOUBLE newVal）; public ： STDMETHOD（get_Area）（DOUBLE * pAreaVal）; STDMETHOD（get_Centroid）（ICartoPoint ** pCentroidVal）; STDMETHOD（get_GeometryType）（cartoGeometryType * pTypeVal）; STDMETHOD（get_NumGeometries）（LONG * pNumberVal）; STDMETHOD（get_NumPoints）（LONG * pNumberVal）; STDMETHOD（get_Coordinates）（ICartoCoordinate ** pVal）; private ： Point * m_pPoint; 坐标* m_pCoordinate; }; OBJECT_ENTRY_AUTO（ __ uuidof （CartoPoint），CCartoPoint） * .cpp文件 STDMETHODIMP CCartoPoint :: get_X（DOUBLE * pVal） { return S_OK; } STDMETHODIMP CCartoPoint :: put_X（DOUBLE newVal） { return S_OK; } STDMETHODIMP CCartoPoint :: get_Y（DOUBLE * pVal） { return S_OK; } STDMETHODIMP CCartoPoint :: put_Y（DOUBLE newVal） { return S_OK; } STDMETHODIMP CCartoPoint :: get_Area（DOUBLE * pAreaVal） { return S_OK; } STDMETHODIMP CCartoPoint :: get_Centroid（ICartoPoint ** pCentroidVal） { CCartoPoint pt; return S_OK; } STDMETHODIMP CCartoPoint :: get_GeometryType（cartoGeometryType * pTypeVal） { return S_OK; } STDMETHODIMP CCartoPoint :: get_NumGeometries（LONG * pNumberVal） { return S_OK; } STDMETHODIMP CCartoPoint :: get_NumPoints（LONG * pNumberVal） { return S_OK; } STDMETHODIMP CCartoPoint :: get_Coordinates（ICartoCoordinate ** pVal） { return S_OK; } 解决方案 抽象类的想法是限制其实例化。这样的类不是为了拥有它的实例而设计的，它被设计成在某些派生类中用作基类，其中一些也可以保持抽象。抽象类可能有纯抽象函数（它们的占位符在虚拟表中，但不是实现，即使它们实际上在其他函数中使用，因此使用这些类的实例将是危险的。但是，它不是必需的;类可以是设计抽象的，它的一些功能可以是虚拟的但是可以实现（伪抽象或非抽象）。 -SA 我没有检查你是否缺少任何API但是类定义的ATL_NO_VTABLE规范告诉编译器该类不会被实例化。 [如果你解决了这个问题，仍然可能有一个或多个需要实现的API ...] I create a ATL project with Visual Studio 2010, and add a ATL simple object class in this project. There is no any error during the building process. But when I declare a class object, such as CCartoPoint pt, I get the error message "error C2259: 'CCartoPoint' : cannot instantiate abstract class"In the following codes, the error message is from the method 'STDMETHODIMP CCartoPoint::get_Centroid( ICartoPoint** pCentroidVal)'.I have checked the the numbers of methods in IDL file, in .h file and the .cpp file is same.The *.IDL file:[object,uuid(14428BC6-A897-4268-8FFD-B4947DEDDFC6),dual,nonextensible,pointer_default(unique)]interface ICartoPoint : IDispatch{[propget, id(2)] HRESULT X([out, retval] DOUBLE* pVal);[propput, id(2)] HRESULT X([in] DOUBLE newVal);[propget, id(3)] HRESULT Y([out, retval] DOUBLE* pVal);[propput, id(3)] HRESULT Y([in] DOUBLE newVal);};[object,uuid(238155D0-220A-4BFA-90D2-46E27461E314),dual,nonextensible,pointer_default(unique)]interface ICartoGeometry : IDispatch{[propget, id(1)] HRESULT Area([out, retval] DOUBLE* pAreaVal);[propget, id(2)] HRESULT Centroid([out, retval] ICartoPoint** pCentroidVal);[propget, id(3)] HRESULT GeometryType([out, retval] cartoGeometryType* pTypeVal);//[propget, id(4)] HRESULT Coordinates([out, retval] ICartoCoordinate** pCdsVal,[out] DOUBLE* pCountVal);[propget, id(5)] HRESULT NumGeometries([out, retval] LONG* pNumberVal);[propget, id(6)] HRESULT NumPoints([out, retval] LONG* pNumberVal);[propget, id(7)] HRESULT Coordinates([out, retval] ICartoCoordinate** pVal);};The *.h fileclass ATL_NO_VTABLE CCartoPoint :public CComObjectRootEx<CComSingleThreadModel>,public CComCoClass<CCartoPoint, &CLSID_CartoPoint>,public IDispatchImpl<ICartoPoint, &IID_ICartoPoint, &LIBID_GeometryObjectLib, /*wMajor =*/ 1, /*wMinor =*/ 0>, public IDispatchImpl<ICartoGeometry, &IID_ICartoGeometry, &LIBID_GeometryObjectLib, /*wMajor =*/ 1, /*wMinor =*/ 0>{public:CCartoPoint(){m_pCoordinate = new Coordinate(0,0);GeometryFactory factory;m_pPoint = factory.createPoint(*m_pCoordinate);}CCartoPoint(DOUBLE x, DOUBLE y){m_pCoordinate = new Coordinate(x,y);GeometryFactory factory;m_pPoint = factory.createPoint(*m_pCoordinate);}DECLARE_REGISTRY_RESOURCEID(IDR_CARTOPOINT)BEGIN_COM_MAP(CCartoPoint)COM_INTERFACE_ENTRY(ICartoPoint)COM_INTERFACE_ENTRY2(IDispatch,ICartoPoint)COM_INTERFACE_ENTRY(ICartoGeometry)END_COM_MAP()DECLARE_PROTECT_FINAL_CONSTRUCT()HRESULT FinalConstruct(){return S_OK;}void FinalRelease(){}public:STDMETHOD(get_X)(DOUBLE* pVal);STDMETHOD(put_X)(DOUBLE newVal);STDMETHOD(get_Y)(DOUBLE* pVal);STDMETHOD(put_Y)(DOUBLE newVal);public:STDMETHOD(get_Area)(DOUBLE* pAreaVal);STDMETHOD(get_Centroid)( ICartoPoint** pCentroidVal);STDMETHOD(get_GeometryType)( cartoGeometryType* pTypeVal);STDMETHOD(get_NumGeometries)(LONG* pNumberVal);STDMETHOD(get_NumPoints)( LONG* pNumberVal);STDMETHOD(get_Coordinates)(ICartoCoordinate** pVal);private:Point* m_pPoint;Coordinate* m_pCoordinate;};OBJECT_ENTRY_AUTO(__uuidof(CartoPoint), CCartoPoint)The *.cpp fileSTDMETHODIMP CCartoPoint::get_X(DOUBLE* pVal){return S_OK;}STDMETHODIMP CCartoPoint::put_X(DOUBLE newVal){return S_OK;}STDMETHODIMP CCartoPoint::get_Y(DOUBLE* pVal){return S_OK;}STDMETHODIMP CCartoPoint::put_Y(DOUBLE newVal){return S_OK;}STDMETHODIMP CCartoPoint::get_Area(DOUBLE* pAreaVal){return S_OK;}STDMETHODIMP CCartoPoint::get_Centroid( ICartoPoint** pCentroidVal){CCartoPoint pt;return S_OK;}STDMETHODIMP CCartoPoint::get_GeometryType( cartoGeometryType* pTypeVal){return S_OK;}STDMETHODIMP CCartoPoint::get_NumGeometries(LONG* pNumberVal){return S_OK;}STDMETHODIMP CCartoPoint::get_NumPoints( LONG* pNumberVal){return S_OK;}STDMETHODIMP CCartoPoint::get_Coordinates(ICartoCoordinate** pVal){return S_OK;} 解决方案 The idea of abstract class is to limit its instantiation. Such class is not designed for having instances of it, it is designed to be used as a base class in some derived classes, some of which also may remain abstract. And abstract class may have pure abstract functions (which have their placeholder in a virtual table, but not implementation, even though they are actually used in other functions, so using instances of such classes would be dangerous. Formally, however, it's not required; a class can be abstract by design, and some functions of it can be virtual but implemented (pseudo-abstract or non-abstract).—SAI didn't check if you are missing any APIs but the ATL_NO_VTABLE spec on the class definition tells the compiler that the class will not be instantiated.[If you fix that, there still might be one or more APIs that need to be implemented...] 这篇关于错误C2259：无法实例化抽象类的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！