c++ - 为什么VC2008认为这个类是抽象的？

Question

我正在编写一些代码来使用 DirectShow 处理来自某些摄像头的视频输入，因此我必须实现 ISampleGrabberCB。

我实现接口(interface)的类编译正常，但是当我尝试实例化它时，编译器引发“error C2259: 'SampleGrabberCB': cannot instantiate abstract class”。

这是我正在实现的接口(interface):

interface ISampleGrabberCB : public IUnknown {
    virtual STDMETHODIMP SampleCB( double SampleTime, IMediaSample *pSample ) = 0;
    virtual STDMETHODIMP BufferCB( double SampleTime, BYTE *pBuffer, long BufferLen ) = 0;
};

这是我的 SampleGrabberCB header :

#pragma once

#include "stdafx.h"

class SampleGrabberCB : public ISampleGrabberCB {
private:

    int                 _refCount;
    DShowCaptureDevice* _parent;

public:
//  SampleGrabberCB();
    SampleGrabberCB(DShowCaptureDevice* parent);
    ~SampleGrabberCB();

    virtual STDMETHODIMP BufferCB(double sampleTime, BYTE* pBuffer, long bufferLen);
    virtual STDMETHODIMP SampleCB(double sampleTime, IMediaSample * pSample, long bufferLen);

#pragma region IUnknown

    virtual HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, void** ppv) {

        if( riid == IID_ISampleGrabberCB || riid == IID_IUnknown ) {

            *ppv = (void *) static_cast<ISampleGrabberCB*> ( this );
            return NOERROR;
        }

        return E_NOINTERFACE;

    }

    virtual ULONG STDMETHODCALLTYPE AddRef() {
        return ++_refCount;
    }

    virtual ULONG STDMETHODCALLTYPE Release() {
        int n = --_refCount;
        if (n &lt;= 0) {
            delete this;
        }
        return n;
    }

#pragma endregion
};

这是 SampleGrabberCB.cpp 的实现:

#include "StdAfx.h"
#include "SampleGrabberCB.h"

//SampleGrabberCB::SampleGrabberCB() {
//  _parent = NULL;
//}

SampleGrabberCB::SampleGrabberCB(DShowCaptureDevice* parent) {

    _parent = parent;
}

SampleGrabberCB::~SampleGrabberCB() {
}

STDMETHODIMP SampleGrabberCB::BufferCB(double sampleTime, BYTE *pBuffer, long bufferLen) {
    // dummy value for now
    return -50;
}

STDMETHODIMP SampleGrabberCB::SampleCB(double sampleTime, IMediaSample *pSample, long bufferLen) {
    // dummy value for now
    return 100;
}

下面是我的使用方法:

SampleGrabberCB* callback = new SampleGrabberCB(device);

有什么想法吗？谢谢!

Answer 1

接口(interface)中声明的

SampleCB 没有 SampleGrabberCB 类中存在的第三个参数 (bufferLen)。