QueryInterface, AddRef, Release

IUnknown.cpp

#include <objbase.h>
#include <iostream>

interface IX : IUnknown {
  virtual void Fx() = 0;
};

interface IY : IUnknown {
  virtual void Fy() = 0;
};

interface IZ : IUnknown {
  virtual void Fz() = 0;
};

// {EDCC3AD9-E7ED-428F-ABF2-D4095E120315}
static const IID IID_IX = {0xedcc3ad9,
                           0xe7ed,
                           0x428f,
                           {0xab, 0xf2, 0xd4, 0x9, 0x5e, 0x12, 0x03, 0x15}};
// {5EFDAA44-B1C7-4F45-B7B8-E94C7A6E43B6}
static const IID IID_IY = {0x5efdaa44,
                           0xb1c7,
                           0x4f45,
                           {0xb7, 0xb8, 0xe9, 0x4c, 0x7a, 0x6e, 0x43, 0xb6}};
// {D89214D1-781E-4812-942A-76F600692E54}
static const IID IID_IZ = {0xd89214d1,
                           0x781e,
                           0x4812,
                           {0x94, 0x2a, 0x76, 0xf6, 0x00, 0x69, 0x2e, 0x54}};

class CA : public IX, public IY {
  virtual HRESULT STDMETHODCALLTYPE
      QueryInterface(REFIID riid, _COM_Outptr_ void **ppvObject);
  virtual ULONG STDMETHODCALLTYPE AddRef();
  virtual ULONG STDMETHODCALLTYPE Release();

  virtual void Fx() { std::cout << "Fx" << std::endl; }
  virtual void Fy() { std::cout << "Fy" << std::endl; }
  virtual void Fz() { std::cout << "Fz" << std::endl; }

 public:
  CA() : ref_count_(0) {}

 private:
  ULONG ref_count_;
};

HRESULT STDMETHODCALLTYPE
CA::QueryInterface(REFIID riid, _COM_Outptr_ void **ppvObject) {
  if (riid == IID_IUnknown) {
    *ppvObject = static_cast<IX *>(this);
  } else if (riid == IID_IX) {
    *ppvObject = static_cast<IX *>(this);
  } else if (riid == IID_IY) {
    *ppvObject = static_cast<IY *>(this);
  } else {
    *ppvObject = NULL;
    return E_NOINTERFACE;
  }
  (reinterpret_cast<IUnknown *>(*ppvObject))->AddRef();
  return S_OK;
}

ULONG STDMETHODCALLTYPE CA::AddRef() {
  return InterlockedIncrement(&ref_count_);
}

ULONG STDMETHODCALLTYPE CA::Release() {
  if (InterlockedDecrement(&ref_count_) == 0) {
    delete this;
    return 0;
  }
  return ref_count_;
}

IUnknown *CreateInstance() {
  IUnknown *pI = static_cast<IX *>(new CA);
  pI->AddRef();
  return pI;
}

int main() {
  HRESULT hr = S_OK;
  IUnknown *pIUnknown = CreateInstance();

  IX *pIX = NULL;
  hr = pIUnknown->QueryInterface(IID_IX, (void **)&pIX);
  if (SUCCEEDED(hr)) {
    pIX->Fx();
    pIX->Release();
  }

  IZ *pIZ = NULL;
  hr = pIUnknown->QueryInterface(IID_IZ, (void **)&pIZ);
  if (SUCCEEDED(hr)) {
    pIZ->Fz();
    pIZ->Release();
  } else {
    std::cout << "Couldn't get interface IID_IZ" << std::endl;
  }

  pIUnknown->Release();

  return 0;
}