智能指针

一个智能指针实际上就是重载了操作符"->"的类。智能指针类包含指向另外一个对象的指针。当用户调用智能指针上的"->"操作符时，智能指针将把此调用委托或转发给它所包含的指针所指的对象。智能接口指针是一个智能指针，它所包含的指针指向一个接口。
COM接口智能指针类CComPtr:
template <class T>
class CComPtr
{
public:
 typedef T _PtrClass;
 CComPtr()
 {
  p=NULL;
 }
 CComPtr(T* lp)
 {
  if ((p = lp) != NULL)
   p->AddRef();
 }
 CComPtr(const CComPtr<T>& lp)
 {
  if ((p = lp.p) != NULL)
   p->AddRef();
 }
 ~CComPtr()
 {
  if (p)
   p->Release();
 }
 void Release()
 {
  IUnknown* pTemp = p;
  if (pTemp)
  {
   p = NULL;
   pTemp->Release();
  }
 }
 operator T*() const
 {
  return (T*)p;
 }
 T& operator*() const
 {
  ATLASSERT(p!=NULL);
  return *p;
 }
 //The assert on operator& usually indicates a bug.  If this is really
 //what is needed, however, take the address of the p member explicitly.
 T** operator&()
 {
  ATLASSERT(p==NULL);
  return &p;
 }
 _NoAddRefReleaseOnCComPtr<T>* operator->() const
 {
  ATLASSERT(p!=NULL);
  return (_NoAddRefReleaseOnCComPtr<T>*)p;
 }
 T* operator=(T* lp)
 {
  return (T*)AtlComPtrAssign((IUnknown**)&p, lp);
 }
 T* operator=(const CComPtr<T>& lp)
 {
  return (T*)AtlComPtrAssign((IUnknown**)&p, lp.p);
 }
 bool operator!() const
 {
  return (p == NULL);
 }
 bool operator<(T* pT) const
 {
  return p < pT;
 }
 bool operator==(T* pT) const
 {
  return p == pT;
 }
 // Compare two objects for equivalence
 bool IsEqualObject(IUnknown* pOther)
 {
  if (p == NULL && pOther == NULL)
   return true; // They are both NULL objects

  if (p == NULL || pOther == NULL)
   return false; // One is NULL the other is not

  CComPtr<IUnknown> punk1;
  CComPtr<IUnknown> punk2;
  p->QueryInterface(IID_IUnknown, (void**)&punk1);
  pOther->QueryInterface(IID_IUnknown, (void**)&punk2);
  return punk1 == punk2;
 }
 void Attach(T* p2)
 {
  if (p)
   p->Release();
  p = p2;
 }
 T* Detach()
 {
  T* pt = p;
  p = NULL;
  return pt;
 }
 HRESULT CopyTo(T** ppT)
 {
  ATLASSERT(ppT != NULL);
  if (ppT == NULL)
   return E_POINTER;
  *ppT = p;
  if (p)
   p->AddRef();
  return S_OK;
 }
}
在做语音软件开发的时候接触到智能指针的概念，例如要用到以下的代码:
CComPtr<ISpRecoContext> cpRecoCtxt;
CComPtr<ISpRecoGrammar> cpGrammar;
CComPtr<ISpVoice> cpVoice;