错误C2259：无法实例化抽象类 [英] error C2259: cannot instantiate abstract class
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
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（< span class =code-digit> 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（）
{
}
< span class =code-keyword> 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 file
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 = 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 file
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
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).
—SA
I 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IT屋！
查看全文
