Re: Pointers, auto-pointers, etc.

Lance Diduck <>
Thu, 4 Dec 2008 18:12:57 CST
On Dec 3, 6:53 pm, Lance Diduck <> wrote:

On Dec 1, 5:08 pm, Ulrich Eckhardt <> wrote:

Give them this sample code and ask them to improve it using std::auto_ptr.
Actually, there are lots of ways this code can be improved, and some will
be easy when touching the code anyway.

Solutions in the next days, unless anyone else wants to jump in. ;)

My version:
struct base
        virtual ~base() {}
        //two clone functions, made safe
        template<class T> std::auto_ptr<T>clone()const{
                //dynamic_cast to handle virtual base class case
                //usually optimized away
                return std::auto_ptr<T>(dynamic_cast<T*>(clone_imp()));
                return std::auto_ptr<base>(clone_imp());
//not safe to call stand-alone, not in public interface
        virtual base* clone_imp() const = 0;};

struct derived1: virtual base
        base* clone_imp() const
        { return new derived1(*this); }};

struct derived2: base
        base* clone_imp() const
        { return new derived2(*this); }


void foo(){
     derived2 d2;
     d2.clone();//return value still deleted
     derived1 d1;
     //std::auto_ptr<derived1> cd2(d1.clone());//does not compile
     std::auto_ptr<derived1> cd1=d1.clone<derived1>();
     //std::auto_ptr<derived2> cd2(d2.clone<derived1>());//BOOM

     std::auto_ptr<derived1> cd2(d2.clone<derived1>());



Actaully, that implementation has a leak:
It should read
template<class T> std::auto_ptr<T>clone()const{
    std::auto_ptr<base> tmp(clone_imp());
        return std::auto_ptr<T>(p);
    return std::auto_ptr<T>();

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