forced1.c

this is a gcc file, you can download it and learn its usetility, for further detail please look at t

// { dg-do run }

// Test that forced unwinding runs all cleanups.  Also tests that
// rethrowing doesn't call the exception object destructor.

#include <unwind.h>
#include <stdlib.h>

static int test = 0;

static _Unwind_Reason_Code
force_unwind_stop (int version, _Unwind_Action actions,
                   _Unwind_Exception_Class exc_class,
                   struct _Unwind_Exception *exc_obj,
                   struct _Unwind_Context *context,
                   void *stop_parameter)
{
  if (actions & _UA_END_OF_STACK)
    {
      if (test != 15)
        abort ();
      exit (0);
    }

  return _URC_NO_REASON;
}

static void
force_unwind_cleanup (_Unwind_Reason_Code, struct _Unwind_Exception *)
{
  abort ();
}

static void force_unwind ()
{
  _Unwind_Exception *exc = new _Unwind_Exception;
  exc->exception_class = 0;
  exc->exception_cleanup = force_unwind_cleanup;

#ifndef __USING_SJLJ_EXCEPTIONS__
  _Unwind_ForcedUnwind (exc, force_unwind_stop, 0);
#else
  _Unwind_SjLj_ForcedUnwind (exc, force_unwind_stop, 0);
#endif

  abort ();
}

struct S
{
  int bit;
  S(int b) : bit(b) { }
  ~S() { test |= bit; }
};
  
static void doit ()
{
  try {
    S four(4);

    try {
      S one(1);
      force_unwind ();
  
    } catch(...) { 
      test |= 2;
      throw;
    }

  } catch(...) {
    test |= 8;
    throw;
  }
}

int main()
{ 
  doit ();
  abort ();
}