TITLE: Destructor invocation upon exit


PROBLEM: rad2r@uvacs.cs.Virginia.EDU (Robert DeLine)


Sorry for this novice question, but when I call exit() from a program compiled
using g++ 2.1, the destructors for my objects don't get called.  This doesn't
surprise me too much, but is this correct?  Does the ARM mention what should
happen when exit() is called?  What if the program is ended due to an uncaught
exception?  If destructors _are_ called when leaving via an uncaught exception,
perhaps this is a better way than calling exit() to leave from deep inside a
program?


RESPONSE: rmartin@thor.Rational.COM (Bob Martin), 4 Sept 92

The destructors for static objects should be invoked when you call
exit.  However the destructors for objects which are declared as
'auto' variables (on the stack) in the function which calls exit,
probably will not get invoked.  For example.

main()
{
  MyClass A;
  static MyClass B;

  exit();
}


The destructor for B should be invoked.  But the destructor for A
probably will not.  I say probably, because a clever compiler might be
able to figure out that, upon exit, the enclosing stack frames should
be destroyed.

The definition of the exception feature says that all destructors for
objects created as auto variables between the throw and the catch will
be invoked.  Thus, "exit" does not behave the way an exception would.
Presumably, an uncaught exception will be "caught" by the code that
calls main.  Thus, destructors will most likely be invoked for
uncaught exceptions.

I agree, when exceptions are implemented, the present a better
mechanisms for exitting a program than embedded calls to 'exit' do.
And remember, never use gotos.


RESPONSE: steve@taumet.com (Steve Clamage)

Auto objects are NOT destroyed when exit() is called, only static
objects which have been constructed.  My copy of the ARM is not handy,
and I don't remember whether the bit about auto objects is clearly
stated there.  It is made explicit in the C++ Committee Working Paper,
and it is very safe to assume the final Standard will say that.