porting ostream::opfx / osfx from Unix to Linux

I am porting some C++ code from Unix to Linux (Red Hat).

I have run into the following pattern:

ostream& myfunction(ostream& os)
{
  if (os.opfx())
  {
    os << mydata;
    os.osfx();
  }
  return os;
}

The functions opfx and osfx are not available under Red Hat 4.5. I saw a suggestion here to use the ostream::sentry functionality:

ostream& myfunction_ported(ostream& os)
{
  ostream::sentry ok(os);
  if (ok)
  {
    os << mydata;
  }
  return os;
}

I see from here that the purpose of opfx is to verify the stream state before flushing it and continuing.

My questions:

I thought the ostream functions already checked the stream state before operating on the stream. Is this true? Was this not true at some point?

Is replacing opfx with sentr开发者_开发问答y necessary? What does sentry give me that operator<< doesn't give me already?

---

Any existing inserter (unless it's really horribly buggy) is already doing to create a sentry object, so as long as your do your work via an existing inserter, you don't need to create a sentry object yourself.

You do need to create a sentry object when you write your data directly to the stream buffer on your own, without help from any existing inserter (i.e., when you're not using anything else that'll create a sentry for you).

For this code, you can just eliminate creating the sentry objects completely and do something like:

ostream& myfunction(ostream& os)
{
    return os << mydata;
}

Note that the existing code was declared to return an ostream &, but didn't seem to actually return anything.