Re: MSVC++ 2005 bug

From:

Alex Blekhman <xfkt@oohay.moc>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 07 Jun 2007 19:08:11 +0300

Message-ID:

<uzilN4RqHHA.1212@TK2MSFTNGP05.phx.gbl>

Larry Smith wrote:

There is a bug in msvc++ 2005 when running the code below, compiled in
release mode:

void foo(int) {
  throw "error";
}

void bar()
{
  int a = 0;
  try
  {
      foo(a++);
  } catch (...) {
      cout << "a=" << a;
  }
}

This will, in release mode, output "a=0", when it should be "a=1".
Guess that the optimization tried to save a temporary by incrementing
'a' after the function call.

It might actually qualify as an error after all though the rule might be
tricky to pin down (the standard isn't always clear on all matters but I
haven't looked). I'm speculating that "a" need not be incremented until the
next sequence point is encountered which I suspect is the end of the
function call itself.

Yes, function call operator is a sequence point. All
subexpressions before this must be evaluated and all _side
effects completed_. Increment of `a' is such side effect,
which must be completed before entering function's body.

Alex