New istreambuf_iterator debug check

[Petr Ovtchenkov]

On Wed, 24 Jan 2018 17:39:59 +0100
François Dumont <frs.dumont@gmail.com> wrote:

> Hi
> 
>      I'd like to propose this new debug check. Comparing with non-eos 
> istreambuf_iterator sounds like an obvious coding mistake.
> 
>      I propose it despite the stage 1 as it is just a new debug check, 
> it doesn't impact the lib in normal mode.
> 
>      Tested under Linux x86_64, ok to commit ?
> 
> François
> 

       bool
       equal(const istreambuf_iterator& __b) const
-      { return _M_at_eof() == __b._M_at_eof(); }
+      {
+	bool __this_at_eof = _M_at_eof();
+	bool __b_at_eof = __b._M_at_eof();
+
+	__glibcxx_requires_cond(__this_at_eof || __b_at_eof, _M_message(
+	  "Abnormal comparison to non-end-of-stream istreambuf_iterator"));
+	return __this_at_eof == __b_at_eof;
+      }

Looks strange for me. It is legal and possible that istreambuf_iterator
will be in EOF state.

--

  - ptr