[Bug libstdc++/12790] New: basic_filebuf doesn't handle stateful encodings

["peturr02 at ru dot is" <gcc-bugzilla at gcc dot gnu dot org>]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12790

           Summary: basic_filebuf doesn't handle stateful encodings
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: peturr02 at ru dot is
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu

basic_filebuf currently doesn't handle stateful encodings. In particular:

1) codecvt::unshift is not called from seekoff, seekpos and close.

2) seekoff and seekpos don't store the current state in the returned object.

3) seekpos doesn't retrieve the state from the argument.

4) seekoff doesn't set the state to the initial state on seek-to-beginning.