oreore simple shared_ptr

shared_ptr.h

#ifndef UTIL_SHARED_PTR_H_INCLUDED
#define UTIL_SHARED_PTR_H_INCLUDED

// for swap in C++03
#include <algorithm>

// for swap in C++11
#include <utility>

#include <new>

// simple shared ownership pointer
template<class T>
class shared_ptr {
  T* p_;
  int* pn_;

public:
  shared_ptr() : p_(0), pn_(0) { }
  ~shared_ptr() {
    if (pn_ && --*pn_ == 0) {
      delete p_;
      delete pn_;
    }
  }

  explicit shared_ptr(T* p) : p_(p) {
    if (p) {
      try {
        pn_ = new int(1);
      } catch (...) {
        delete p;
        throw;
      }
    } else {
      pn_ = 0;
    }
  }

  shared_ptr(const shared_ptr& p)
    : p_(p.p_), pn_(p.pn_) {
    if (pn_) ++*pn_;
  }

  shared_ptr& operator=(const shared_ptr& p) {
    shared_ptr<T> tmp(p);
    tmp.swap(*this);
    return *this;
  }
  void reset(T* p = 0) {
    shared_ptr<T> tmp(p);
    tmp.swap(*this);
  }
  void swap(shared_ptr& p) {
    std::swap(p_, p.p_);
    std::swap(pn_, p.pn_);
  }

  T* get() const { return p_; }
  T* operator->() const { return p_; }
  T& operator*() const { return *p_; }
  operator bool() const { return p_ != 0; }

  // for debug
  int count() const { return pn_ ? *pn_ : 0; }
};

#endif // UTIL_SHARED_PTR_H_INCLUDED