Re: auto_ptr vs. boost shared_ptr

James Kanze <kanze.james@neuf.fr> wrote:


  Does your GC handle things like
  
  struct larger_than_10
  {
      bool operator () (int *p) {return *p > 10;}
  };
 
  struct create_ptr()
  {
        int i;
        create_ptr():i(1){};
        int * operator () () {return new int(i++);}
  };
 
  struct kill
  {
       void operator () (int *x) {delete x;}
  };
  int main()
  {
        std::vector<int *> data;
        std::generate_n(std::back_inserter(data),1000,create_ptr());

        std::vector<int *>::iterator last =
           std::remove_if
           (
              data.begin(),
              data.end(),
              larger_than_10()
           );
        std::for_each(last,data.end(),kill());
        data.erase(last,data.end());
   }

 remove_if blindly overwrites the int *'s so the deleted ones are either
never deleted until the os takes over, or are deleted mutliple times.
fine of the int *'s are not on the heap but statically allocated but
it is a pitfall someone that does not examine the actual code of
remove_if will not think of.

// For is a forward iterator.
template <class For,class Pred>
For remove_if(For begin,For end, Rred pred)
{
    For last(begin);
    while(begin != end)
    {
        if(!pred(*begin))
        {
           *last = *begin;
           ++last;
        }
        ++begin;
    }
    return last;
}

looks like a reference implementation to me of remove_if. If your GC
handles overwrites like this, its ok, but using raw ptrs in any stl
container is a recipe for disaster, if the access to the container is
not controlled, and kept away from the 'user'.

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