///////////////////////////////////////////////////////////////////////
//  auto_ptr.cpp - demonstrate use of auto_ptr class from <utility>  //
//                                                                   //
//  Jim Fawcett, CSE687 - Object Oriented Design, Spring 2001        //
///////////////////////////////////////////////////////////////////////
/*
    The auto_ptr class manages ownership of a single object allocated
    on the heap.  When an auto_ptr is constructed, it takes ownership
    of pointer passed in its constructor argument.  That implies that:
    - auto_ptr assignment transfers ownership to the assignee.
    - auto_ptr will destruct an object it owns when it goes out of
      scope.  That includes when an exception is thrown.

    Copy construction and assignment cause the source to change, e.g.,
    the source auto_ptr loses ownership.  This is not allowed for STL
    containers, so you can't use them there.

    You can't use auto_ptrs for arrays.  The auto_ptr destructor calls
    delete, not delete [], so array ownership does not work.  Fortunately
    it fails at compile time, in case you forget.
*/

#pragma warning(disable : 4786)
#include <iostream>
#include <memory>     // here is where auto_ptr is declared
using namespace std;

//----< an object defined only for this demonstration >------------

class test {

  public:
    test() { cout << "\n  constructing a test object"; }
    ~test() { cout << "\n  destroying a test object"; }
    void accept(const string &s) { testStr = s; }
    void say() { cout << "\n  " << testStr.c_str(); }
  private:
    string testStr;
};

//----< function to test auto_ptr when an exception is thrown >----

template <class T>
void testAutoPtr(auto_ptr<T> apT) /*thow(exception)*/ {

  apT->say();
  cout << "\n  Now we are going to throw an exception";
  throw exception("in exception handler");
}

//
//----< test stub >------------------------------------------------

void main() {

  cout << "\n  Demonstrate use of auto_ptr objects "
       << "\n =====================================\n";

  auto_ptr<test> pTest(new test);
  try {
    pTest->accept("this is a test input");
    testAutoPtr(pTest);
  }
  //////////////////////////////////////////////////////////////////
  // auto_ptr.get() is supposed to return NULL when it does not   //
  // have ownership.  As you will see by looking at the display   //
  // of this handler, Visual C++ auto_ptr does not conform.       //
  //////////////////////////////////////////////////////////////////
  catch(exception &e) { 
    cout << "\n  " << e.what() << "\n"; 
    if(pTest.get() == NULL)
      cout << "  auto_ptr is compliant with the C++ standard\n";
    else
      cout << "  auto_ptr is not compliant with the C++ standard\n";
  }
  cout << "\n\n";
}