Object-Oriented Suicide or delete this;

问题

The following code compiled with MSVC9.0 runs and outputs Destructor four times, which is logical.

#include <iostream>
class SomeClass
{
public:
   void CommitSuicide()
   {
      delete this;
   }
   void Reincarnate()
   {
      this->~SomeClass();
      new (this) SomeClass;
   }
   ~SomeClass()
   {
      std::cout  << "Destructor\n";
   }
};

int main()
{
   SomeClass* p = new SomeClass;
   p->CommitSuicide();
   p =  new SomeClass;
   p->Reincarnate();
   p->~SomeClass(); //line 5
   p->CommitSuicide();
}

I think the first 4 lines of code in main do not result in undefined behavior (although not entirely sure about the delete this; thing). I would like to have a confirmation or < placeholder for confirmation's antonym > of that. But I have serious doubts about lines 5 and 6. It is allowed to explicitly call the destructor, isn't it? But is the lifetime of the object considered to have finished after that? That is, is invocation of another member after the explicit call of the destructor allowed (defined)?

To summarize, which parts of the above code (if any) result in undefined behavior (technically speaking)?

回答1:

p->~SomeClass(); //line 5

p->CommitSuicide(); //line 6

Line (6) definitely invokes Undefined Behaviour.

That is, is invocation of another member after the explicit call of the destructor allowed (defined)?

No! Your assumption is correct.

回答2:

The delete this; is fine. The last p->CommitSuicide(); gives undefined behavior because you already destroyed the object in "line 5".

回答3:

"delete this" is ok as long as you do not attempt to call any code of that object after the deletion (not even the destructor). So a self deleting object shoud only be placed at the heap and shoud have a private destructor to protect from creation on the stack.

I dont know if a direct call to the destructor leads to undefined behaviour but a userdefined delete-operator would'nt get executed.

来源：https://stackoverflow.com/questions/3959634/object-oriented-suicide-or-delete-this

标签

c++

destructor

delete-operator

self-destruction