It seems that MS VC++ 5.0 does not support member templates.
I also think that the implementation for the auto_ptr that comes with it
is not quite working.

Therefore, I have tried to rewrite the auto_ptr without using member
templates
(and without modifying it to much); The code that was removed was
commented with //-.
The code that was added is commented. I would appreciate any feedback on
it,
I am not quite sure I have got it right.

I add here the code. (the code was adapted from "More Effective C++
35 New Ways to Improve Your Programs and Designs" by: Scott Meyers).


///////////////////////////////////////////////////////////////////////////////

template<class X>
class auto_ptr {
    mutable bool owner;
    X* px;
    // template<class Y> friend class auto_ptr;

public:

    // explicit removed so that implicit conversion can take place
    //- explicit auto_ptr(X* p=0)
    auto_ptr(X* p=0)
        : owner(p!=0), px(p) {}

    // template members not supported
    //- template<class Y>
    //- auto_ptr(const auto_ptr<Y>& r)
    auto_ptr(const auto_ptr& r)
        : owner(r.owner), px(r.release()) {}

    // template members not supported
    //- template<class Y>
    //- auto_ptr& operator=(const auto_ptr<Y>& r) {
    auto_ptr& operator=(const auto_ptr& r) {
        if ((void*)&r != (void*)this) {
            if (owner)
                delete px;
            owner = r.owner;
            px = r.release();
        }
        return *this;
    }

    // Added overloaded assignment to auto_ptr from a ptr
    auto_ptr& operator=(X* p) {
        return operator=(auto_ptr<X>(p));
    }

    ~auto_ptr()           { if (owner) delete px; }

    X& operator*()  const { return *px; }
    X* operator->() const { return px; }
    X* get()        const { return px; }
    X* release()    const { owner = 0; return px; }

    // Added conversion operator to a ptr
    operator X*() {release(); return px;}
};
///////////////////////////////////////////////////////////////////////////////
// Using auto_ptr
///////////////////////////////////////////////////////////////////////////////


class A {
public:
    int at;
    virtual ~A(){}

};

class B : public A {
public:
    int bt;
    virtual ~B(){}

};

///////////////////////////////////////////////////////////////////////////////
void main()
{

    auto_ptr<A> pa ( new A );
    pa->at = 1;

    auto_ptr<B> pb ( new B );
    pb->at = 2;
    pb->bt = 22;

    pa = pb;
    // pb = pa; // does not work - is OK!

///////////////////////////////////////////////////////////////////////////////
    char ch;
    cout << endl << ">> Press any key to EXIT: "; cin >> ch;
}
///////////////////////////////////////////////////////////////////////////////

--
Cristian Georgescu
_________________________________________________
    Smiths Industries
    Aerospace & Defense Systems
    7-9 Vreeland Road,
    Florham Park, NJ 07932, USA.
_________________________________________________
E-mail: Georgescu_Christian@si.com
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THe auto_ptr that ships with VC5 has a bug which allows to auto_ptr
instances to own the same object with disasterous results. Try the
following program on your implementation to see if you got it right.

Regards,  John.

//-----

/*
** Problem:  auto_ptr template causes double deletion of contained
object.
** Severity:  severe
** Work-around: none
**
** Test Case:  Create an auto ptr instance with a contained object.
**     Create a second auto_ptr instance using copy constructor.
**     Assign the first instance from the second.
** Result:   Two auto_ptr instances own the same datum; heap is
corrupted
**     when the datum is deleted a second time.
**
** Auto_Ptr:  This template, copied from Vc/include/memory, was modified
**     slightly to prevent the double delete.  It is NOT compliant
**     with the standard (IMHO) but this implementation has the
**     following great advantage:
**      The assignment x = y is idempotent
*/

#include <iostream>
#include <memory>
#include <Auto_Ptr.h>
#include <Auto_Ptr_New.h>
using namespace std;


struct T
{
 T() { cerr << "T::T, this==" << (void*)this << endl; }
   ~T() { cerr << "T::~T, this==" << (void*)this << endl; }
};


void test_AP()
{
 Auto_Ptr<T> p( new T );
 Auto_Ptr<T> q( p );
 p = q;
}

void test_ap()
{
 auto_ptr<T> p( new T );
 auto_ptr<T> q( p );
 p = q;
}

void test_APN()
{
 Auto_Ptr_New<T> p( new T );
 Auto_Ptr_New<T> q( p );
 p = q;
}

int main()
{
 cerr << "==> test " << typeid(Auto_Ptr<T >).name() << "\n";
 test_AP ();
 cerr << "==> test " << typeid(Auto_Ptr_New<T >).name() << "\n";
 test_APN ();
 cerr << "==> test " << typeid(auto_ptr<T >).name() << "\n";
 test_ap ();
 return EXIT_SUCCESS;
}
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Cristian Georgescu <Cristian.Georgescu@worldnet.att.net> wrote:

>It seems that MS VC++ 5.0 does not support member templates.

I have used member templates in that compiler. Have you applied (at
least) Service Pack 2?

>I also think that the implementation for the auto_ptr that comes with it
>is not quite working.

That's a different matter, and I don't know either way. It could be
that if you applied SP2 auto_ptr would work.

><MEC++ auto_ptr snipped>

[crossposted and followups set to microsoft.public.vc.language]
--
Mike Enright
menright@cts.com (Email replies cheerfully ignored, use the news group)
http://www.users.cts.com/sd/m/menright/
Cardiff-by-the-Sea, California, USA
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