supersmartpointer.cpp

C++高级编程这本书所附的源代码

#include <map>
#include <iostream>

template <typename T>
class SuperSmartPointer
{
public:
  explicit SuperSmartPointer(T* inPtr);
  ~SuperSmartPointer();

  SuperSmartPointer(const SuperSmartPointer<T>& src);
  SuperSmartPointer<T>& operator=(const SuperSmartPointer<T>& rhs);

  const T& operator*() const;
  const T* operator->() const;
  T& operator*();
  T* operator->();

  operator void*() const { return mPtr; }

protected:
  T* mPtr;
  static std::map<T*, int> sRefCountMap;

  void finalizePointer();
  void initPointer(T* inPtr);
};

template <typename T>
std::map<T*, int>SuperSmartPointer<T>::sRefCountMap;

template <typename T>
SuperSmartPointer<T>::SuperSmartPointer(T* inPtr)
{
  initPointer(inPtr);
}

template <typename T>
SuperSmartPointer<T>::SuperSmartPointer(const SuperSmartPointer<T>& src)
{
  initPointer(src.mPtr);
}

template <typename T>
SuperSmartPointer<T>& 
SuperSmartPointer<T>::operator=(const SuperSmartPointer<T>& rhs)
{
  if (this == &rhs) {
    return (*this);
  }
  finalizePointer();
  initPointer(rhs.mPtr);

  return (*this);
}

template <typename T>
SuperSmartPointer<T>::~SuperSmartPointer()
{
  finalizePointer();
}

template<typename T>
void SuperSmartPointer<T>::initPointer(T* inPtr)
{
  mPtr = inPtr;
  if (sRefCountMap.find(mPtr) == sRefCountMap.end()) {  
    sRefCountMap[mPtr] = 1;
  } else {
    sRefCountMap[mPtr]++;
  }
}

template<typename T>
void SuperSmartPointer<T>::finalizePointer()
{
  if (sRefCountMap.find(mPtr) == sRefCountMap.end()) {
    std::cerr << "ERROR: Missing entry in map!" << std::endl;
    return;
  }
  sRefCountMap[mPtr]--;
  if (sRefCountMap[mPtr] == 0) {
    // no No more references to this object -- delete it and remove from map
    sRefCountMap.erase(mPtr);
    delete mPtr;
  }
}

template <typename T>
const T* SuperSmartPointer<T>::operator->() const
{
  return (mPtr);
}

template <typename T>
const T& SuperSmartPointer<T>::operator*() const
{
  return (*mPtr);
}

template <typename T>
T* SuperSmartPointer<T>::operator->() 
{
  return (mPtr);
}

template <typename T>
T& SuperSmartPointer<T>::operator*() 
{
  return (*mPtr);
}



// Tests follow

class Nothing
{
public:
  Nothing() { sNumAllocations++; }
  ~Nothing() { sNumDeletions++; }

  static int sNumAllocations;
  static int sNumDeletions;
};

int Nothing::sNumAllocations = 0;
int Nothing::sNumDeletions = 0;

int main(int argc, char** argv)
{
  Nothing* myNothing = new Nothing();

  {
    SuperSmartPointer<Nothing> ptr1(myNothing);
    SuperSmartPointer<Nothing> ptr2(myNothing);
  }

  if (Nothing::sNumAllocations != Nothing::sNumDeletions) {
    std::cout << "TEST FAILED: " << Nothing::sNumAllocations <<
      " allocations and " << Nothing::sNumDeletions << 
      " deletions" << std::endl;
  } else {
    std::cout << "TEST PASSED" << std::endl;
  }
}