C++ smart pointer智能指针

  在C++中，程序员可以直接操作内存，给编程增加了不少的灵活性。但是灵活性是有代价的，程序员必须负责自己负责释放自己申请的内存，否则就会出现内存泄露。智能指针就是为了解决这个问题而存在的。它和其他指针没有本质的区别，主要的目的就是为了避免悬挂指针、内存泄露的问题。在这里，我使用对象的应用计数做了一个smart pointer，当一个对象还有引用的时候，就不执行释放内存的操作，当引用计数为0时，就执行内存释放操作，并且将指针重置为NULL。

代码如下：

#include <iostream>
#include <malloc.h>

/*

 desc:   A smart pointer to automatic alloc and dellocat memories.
 author: justinzhang(uestczhangchao@gmail.com).
 time: 2015-1-22 09:44:24

*/

template <class T>
class smartPtr {

public:
  smartPtr() {
    ptr = NULL;
    refCnt = (unsigned *) malloc(sizeof(unsigned));
  }

  smartPtr( T * pt) {

    this->ptr = pt;
    refCnt = (unsigned *) malloc(sizeof(unsigned));
    std::cout << "Enter constructor, refCnt is "<< *refCnt << std::endl;
    *refCnt = 1;

    std::cout << "Leave constructor, refCnt is " << *refCnt << std::endl;

  }

  smartPtr(smartPtr<T> &copy) {

    ptr = copy.ptr;

    refCnt = copy.refCnt;
    std::cout << "Enter copy constructor, refCnt is " << *refCnt << std::endl;

    ++*refCnt;

    std::cout << "Leave copy constructor, refCnt is "<< *refCnt << std::endl;

  }

  smartPtr<T> & operator=(smartPtr<T> &copy) {

    std::cout << "Enter operator=, refCnt is "<< *copy.refCnt << std::endl;

    if(this != &copy) {
      ptr = copy.ptr;
      refCnt = copy.refCnt;
      ++*refCnt;
    }
    std::cout << "Leave operator=, refCnt is " << *refCnt << std::endl;
    return *this;

  }

  ~smartPtr() {

    std::cout << "Enter destructor, refCnt is " << *refCnt << std::endl;

    --*refCnt;

    if(*refCnt == 0 ) {
      std::cout << "In destructor, refCnt is 0 , this pointer will be freed." << std::endl;

      if( NULL != ptr ) {

    delete ptr;
        ptr = NULL;

      }

      if(NULL != refCnt ) {
    free(refCnt);
    refCnt = NULL;
      }

    } else {

      std::cout << "Leave destructor, refCnt is " << *refCnt << std::endl;
    }

  }

  T getValue() {

    return *ptr;
  }

protected:
  T * ptr;
  unsigned *refCnt;

};

int main() {

  int * p = new int[2];

  smartPtr<int > intSmart(p) ;
  smartPtr<int> copySmart(intSmart); // copy constructor will be called.
  smartPtr<int> operatorSmart = intSmart ; // Here the copy consturctor will be called, not the assignment operator.
  operatorSmart = intSmart; // Here the assignment operator will  be called.

  return 0;

}

运行结果如下：