///////////////////////////////////////////////////////////////////////
//  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.

    ---NOTE---
    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("exception thrown in testAutoPtr(...)");
}

//
//----< 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 object speaking");
    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\n  Entering Exception Handler\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";
}