[Moderator's note: this has been
 forwarded to the C++ committee. -moderator.]

Defect Report: Wrong recommendation in DR22
Ref: C++ Standard Library Issues List (Revision 18)
Sec. 27.8.1.7 [lib.ifstream.members]
Issue 22. Member open vs. flags
(For your convenience, I cite DR 22 at the end of this report)

First of all, there is a typo:
basic_ifstream<>::open is meant, not basic_istream<>::open.
The latter has no open, and sec. 27.8.1.7 [lib.ifstream.members] deals
with the first.

I consider the proposed resolution
"A successful open does not change the error state."
wrong. The reasons are:

1. According to the standard, open() shall behave like fopen().
    In more detail:
   basic_ifstream::open() simply calls rdbuf()->open().
   rdbuf() returns a pointer to a basic_filebuf-object.
   You find basic_filebuf::open() in sec 27.8.1.3 [lib.filebuf.members]
   on p 659.
   The document says, that the opening is
   "'as if' by calling std::fopen(s,modstr)"
   Conclusion:
   fopen() and ifstream::open() should have the same behavior.
   fopen() DOES clear the state!

2. Not clearing the state means inconsistent object states.
   Example:
  std::ifstream is("fop.c");
  char c;
  while(!is.eof()) is.get(c);;  // reach eof here, i.e set eof-bit
  is.close();
  std::cout << "reuse of existing ifstream with is.open():\n";
  // consider with and without: is.clear();
  is.open("anotherExistingFile.txt");
  // of course, eof is not reached here! (nonempty file)
  if(is.eof())
    std::cout << "File cannot be read, because it seems to be at EOF,"
               " although there was no read access!"
               " I.e. 'is' is in an inconsistent state!\n";
  else std::cout << "this is ok\n";

Of course, when I open an existing, not empty file for reading, I expect
it not to be at EOF! Following the proposed resolution above means
violating the "principle of least surprise".


I suggest:
In 27.8.1.7 [lib.ifstream.members] paragraph 3, and in 27.8.1.10
[lib.ofstream.members] paragraph 3, under open() effects, add as
the first sentence, i.e. before "Calls rdbuf->open":

 Clears eofbit and failbit.

This would avoid inconsistent object states, would exhibit the expected
behavior (= no surprise), and would also conform to fopen(), as
the standard requires.


Regards

  Uli


***********************************************************************
Issue 22. Member open vs. flags

Section: 27.8.1.7 [lib.ifstream.members]   Status:  DR   Submitter:
Nathan Myers Date: 6 Aug 1998

The description of basic_istream<>::open leaves unanswered questions
about how it responds to or changes flags in the error status for the
stream. A strict reading indicates that it ignores the bits and does not
change them, which confuses users who do not expect eofbit and failbit
to remain set after a successful open. There are three reasonable
resolutions: 1) status quo 2) fail if fail(), ignore eofbit 3) clear
failbit and eofbit on call to open().

Proposed resolution:

In 27.8.1.7 [lib.ifstream.members] paragraph 3, and in 27.8.1.10
[lib.ofstream.members] paragraph 3, under open() effects, add a
footnote:

A successful open does not change the error state.
***********************************************************************
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