class B;

class A {
   B * pb;
public:
   A() : pb(new B()) {}
   ~A()
   {
      delete pb;
      pb = 0;
   }
};

PK>>class B;

PK>>class A {
PK>>   B * pb;
PK>>public:
PK>>   A() : pb(new B()) {}
PK>>   ~A()
PK>>   {
PK>>      delete pb;
PK>>      pb = 0;
PK>>   }
PK>>};
PK>>

J>Это так народ пытается нейтрализовать двойной вызов деструктора

A * a = new A();
a->SomeMethod(); // method uses A::pb
delete a;
a->SomeMethod();

    A a;
    a.~A();
    a.~A();

class A
{
    .......
    B* pb;
    .......
    
    void foo()
    {
        .....
        if(pb) .....
        .....
    }

    ~A()
    {
        .....
        foo();
        .....
        delete pb; pb = 0;
        .....
        foo();
        .....
    }
};

PK>class B;

PK>class A {
PK>   B * pb;
PK>public:
PK>   A() : pb(new B()) {}
PK>   ~A()
PK>   {
PK>      delete pb;
PK>      pb = 0;
PK>   }
PK>};
PK>

class B;

class A {
   B * pb;
public:
   A() : pb(new B()) {}
   ~A()
   {
      delete pb;
      pb = 0;
      CleanupAll();
   }

   void CleanupAll()
   {
   ....
   pb->Cleanup();
   ...
   }
};

3.8/5
...
If the object will be or was of a non-POD class type, the program has undefined behavior if:
— the pointer is used to access a non-static data member or call a non-static member function of the object

Once a destructor is invoked for an object, the object no longer exists; the behavior is undefined if the
destructor is invoked for an object whose lifetime has ended (3.8). [ Example: if the destructor for an automatic
object is explicitly invoked, and the block is subsequently left in a manner that would ordinarily
invoke implicit destruction of the object, the behavior is undefined. ]

class A
{
public:
A(type *p = NULL)
   : ptr(p)
{};

~A()
{
 if(ptr)
 {
   delete ptr;
   ptr = NULL;
 }
};

type *ptr;
};

A some_function()
{
  A a(new type(/*init*/));
  /*some code*/
  return a;
}

void main()
{
  A a = some_function();
}

K>>иногда надо, и с таким сталкивался, когда в деструкторе стоит эвент говорящий что объект уничтожается, а обработчик может обратится к этой переменной, а то и косвенно вызвать деструктор еще раз

TREGDataContainer::~TREGDataContainer()
{
 DEBUG_CODE(m_sobj_is_destroyed=true);

 this->ResetHandlers();

 //отключаемся от уведомлений вложенных объектов
 Folders              .ResetHandlers();
 Persons              .ResetHandlers();
 Things               .ResetHandlers();
 PersonDealRefs       .ResetHandlers();
 ThingDealRefs        .ResetHandlers();
 CommonDocuments      .ResetHandlers();
 Units                .ResetHandlers();
 Deals                .ResetHandlers();
 UnitDealLinks        .ResetHandlers();
 UnitRightLinks       .ResetHandlers();
 DealCMDocLinks       .ResetHandlers();
 UnitCMDocLinks       .ResetHandlers();

 CurrentDeal          .ResetHandlers();
 CurrentThingDealRef  .ResetHandlers();

 DESTROY_COMPONENT()
}//~TREGDataContainer

void TREGDataContainer::ResetHandlers()
{
 OnDataChange                =NULL;
 OnCMDocumentChange          =NULL;
 OnDealChange                =NULL;
 OnUnitChange                =NULL;

 OnCurrentThingDealRefChange =NULL;
}//ResetHandlers

void f()
{
    T t(1);
    T & rt = t;
    // <1> действия с t или rt
    t.~T();
    new (&t) T(2);
    // <2> действия с t или rt
    // автоуничтожение t
}

_wf>void f()
_wf>{
_wf>    T t(1);
_wf>    T & rt = t;
_wf>    // <1> действия с t или rt
_wf>    t.~T();
_wf>    new (&t) T(2);
_wf>    // <2> действия с t или rt
_wf>    // автоуничтожение t
_wf>}
_wf>

12.4/14
...
the behavior is undefined if the destructor is invoked for an object whose lifetime has ended (3.8).
...