Re: A Sample auto_ptr implementation

Ankur Arora <>
Mon, 13 Oct 2008 07:10:23 -0700 (PDT)
Thanks for the reply Kai!
Please see the comments below.

On Oct 13, 2:53 pm, Kai-Uwe Bux <> wrote:

Ankur Arora wrote:

Hi All,

I'm building a sample application that uses a custom auto_ptr
The program crashes with the following output:-

Output (Debug Assertion failed)

         release called
         copy constructor
         aap: ptr2= 10
         aap: ptr3= 20
         aap: ptr3= 10
         aap: exiting app
         Deleting pointee...10
         Deleting pointee...-572662307 (

oblem ?)


Just a data point: your code works for me with output

         release called
         copy constructor
         aap: ptr2= 10
         aap: ptr3= 20
         Inside operator=
         Inside operator=, calling reset
         release called
         reset called
         aap: ptr3= 10
         aap: exiting app
         Deleting pointee...10

So I just have nits:


using namespace std;

It's a bad idea to use using namespace std in a header.



template <class T>
inline MyAutoPtr<T>::~MyAutoPtr()
    cout<<"\n\t Deleting pointee..."<<*pointee;
    delete pointee;

delete will perform its own check for 0. It is required to be a null-op i=


that case.

I did this since removing this check caused the program to crash, even
though I had made pointee equals to 0 in release(), which was used in
the copy constructor.
I'm using visual studio 2008 express edition. You reckon this is a
complier issue?


template<class T>
template<class U>
MyAutoPtr<T>& MyAutoPtr<T>::operator=(MyAutoPtr<U>& rhs)
  cout<<"\n\t Inside operator=";

This if-clause will not compile when T and U are different.

You could use

  if ( this->pointee == rhs.pointee )

instead (I think).

I saw this example in "More Effective C++" by scott meyers. This was
how its used in that book. Here is a code.

template<class T>
class auto_ptr {
  explicit auto_ptr(T *p = 0); // see Item 5 for a
                                            // description of
  template<class U> // copy constructor member
  auto_ptr(auto_ptr<U>& rhs); // template (see Item 28):
                                            // initialize a new
                                            // with any compatible
                                            // auto_ptr
  template<class U> // assignment operator
  auto_ptr<T>& // member template (see
  operator=(auto_ptr<U>& rhs); // Item 28): assign from
                                            // compatible auto_ptr
  T& operator*() const; // see Item 28
  T* operator->() const; // see Item 28
  T* get() const; // return value of current
                                            // dumb pointer
  T* release(); // relinquish ownership of
                                            // current dumb pointer
                                            // return its value
  void reset(T *p = 0); // delete owned pointer;
                                            // assume ownership of p
  T *pointee;
template<class U> // make all auto_ptr
friend class auto_ptr<U>; // friends of one another

template<class T>
inline auto_ptr<T>::auto_ptr(T *p)
: pointee(p)
template<class T>
  inline auto_ptr<T>::auto_ptr(auto_ptr<U>& rhs)
  : pointee(rhs.release())
template<class T>
inline auto_ptr<T>::~auto_ptr()
{ delete pointee; }
template<class T>
  template<class U>
  inline auto_ptr<T>& auto_ptr<T>::operator=(auto_ptr<U>& rhs)
    if (this != &rhs) reset(rhs.release());
    return *this;
template<class T>
inline T& auto_ptr<T>::operator*() const
{ return *pointee; }
template<class T>
inline T* auto_ptr<T>::operator->() const
{ return pointee; }
template<class T>
inline T* auto_ptr<T>::get() const
{ return pointee; }
template<class T>
inline T* auto_ptr<T>::release()
  T *oldPointee = pointee;
  pointee = 0;
  return oldPointee;
template<class T>
inline void auto_ptr<T>::reset(T *p)
  if (pointee != p) {
    delete pointee;
    pointee = p;

Anything wrong with the above ? (would be surprised if there is, as it
came from scott meyers)

Q1. Any problems with the above code ?

It works with g++.

Again, looks like an issue with visual studio 2008 express.

Q2. What is causing operator= not to be called and how to fix it ?

A bug in your compiler?



Kai-Uwe Bux

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