Question

suppose that,we have following code

auto_ptr<T> source() 
{
  return auto_ptr<T>( new T(1) );
}
void sink( auto_ptr<T> pt ) { }
void f()
{
  auto_ptr<T> a( source() );
  sink( source() );
  sink( auto_ptr<T>( new T(1) ) );
  vector< auto_ptr<T> > v;
  v.push_back( auto_ptr<T>( new T(3) ) );
  v.push_back( auto_ptr<T>( new T(4) ) );
  v.push_back( auto_ptr<T>( new T(1) ) );
  v.push_back( a );
  v.push_back( auto_ptr<T>( new T(2) ) );
  sort( v.begin(), v.end() );
  cout << a->Value();
}
class C
{
public:    /*...*/
protected: /*...*/
private:   /*...*/
  auto_ptr<CImpl> pimpl_;

i am interested: What’s good, what’s safe, what’s legal, and what’s not in this code?
as i know about auto_ptr is that,for example following code

#include <iostream>
#include <memory>
using namespace std;

int main(int argc, char **argv)
{
    int *i = new int;
    auto_ptr<int> x(i);
    auto_ptr<int> y;

    y = x;

    cout << x.get() << endl; // Print NULL
    cout << y.get() << endl; // Print non-NULL address i

    return 0;
}

This code will print a NULL address for the first auto_ptr object and some non-NULL address for the second, showing that the source object lost the reference during the assignment (=). The raw pointer i in the example should not be deleted, as it will be deleted by the auto_ptr that owns the reference. In fact, new int could be passed directly into x, eliminating the need for i.
how can i dtermine which line in my code is safe,which is not?

Answer 1

vector<auto_ptr<T>> v;
v.push_back(auto_ptr<T>( new T(3) ));
v.push_back(auto_ptr<T>( new T(4) ));
v.push_back(auto_ptr<T>( new T(1) ));

The standard completely forbids this.