throwing dtors...

From:
"Chris M. Thomasson" <no@spam.invalid>
Newsgroups:
comp.lang.c++
Date:
Wed, 1 Oct 2008 20:25:25 -0700
Message-ID:
<k4XEk.16199$hX5.2021@newsfe06.iad>
Is it every appropriate to throw in a dtor? I am thinking about a simple
example of a wrapper around a POSIX file...
________________________________________________________________________
class file {
  FILE* m_handle;

public:
  // [...];

  ~file() /* throw() */ {
    int const status fclose(m_handle);
    if (status) {
      /* shi% hit the fan:
        http://www.opengroup.org/onlinepubs/007908775/xsh/fclose.html
      /*

      // [what now?]
    }
  }
};
________________________________________________________________________

How to properly handle `EAGAIN' in dtor? Well, what about any error for that
matter? I am a C programmer and only code C++ for fun, and some in-house
projects. If I were really going to create C++ application and release it
into the wild, well, how would you advise me to handle the case above? I am
interested in how throwing in a dtor effects dynamic destruction... Would
something like the following be legal?

<pseudo code!!!!>
_______________________________________________________________
struct throw_from_dtor {
  int const m_status;

public:
  throw_from_dtor(int const status)
   m_status(status) {}

  int get_status() const { return m_status; }
};

class file {
  FILE* m_handle;

public:
  // [ctor];

  ~file() {
    int const status = fclose(m_handle);
    if (status) {
      throw throw_from_dtor(status);
    }
  }
};

int main() {
  file* f = new file();
  try {
    delete f;
  } catch(throw_from_dtor const& e) {
    // handle error from `e.get_status()'
    delete f;
  }
  return 0;
}
_______________________________________________________________

?

or what about using smart pointer...

int main() {
  std::auto_ptr<file> f;
  try {
    f.reset(new file());
  } catch(throw_from_dtor const& e) {
    // handle error from `e.get_status()'
  }
}

?

Please keep in mind that refusing to not handle an error from `fclose' could
resule is HORRIBLE things down the road... Think massive data lost...
Perhaps __permanent__ data-! OUCH!!!

;^/

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