[Boost-bugs] [Boost C++ Libraries] #10809: Seeking breaks iostreams::restriction<std::istream> internal state

Subject: [Boost-bugs] [Boost C++ Libraries] #10809: Seeking breaks iostreams::restriction<std::istream> internal state
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-11-21 01:47:49

#10809: Seeking breaks iostreams::restriction<std::istream> internal state
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 Reporter:  chris42f@…        |      Owner:  turkanis
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  iostreams
  Version:  Boost 1.55.0      |   Severity:  Problem
 Keywords:                    |
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 As in the attached test case, calling seekg() on a restricted istream
 appears to break the internal state such that more characters can be
 extracted than expected.

 I've done some digging around, and I think this is because the restriction
 device does a seek relative to std::ios_base::cur, which returns -1 from
 the underlying implementation:  Calling std::streambuf::pubseekoff() with
 way = ios_base::cur and which = (ios_base::in | ios_base::out) fails
 according to the C++ standard section 27.8.2.4.

 When fixing this, it's worth noting that calling pubseekoff() will also
 fail with libstdc++ if it's passed (ios_base::in | ios_base::out) when the
 stream buffer has only an output buffer or input buffer, but not both.

 Tested with g++-4.6.3 and g++-4.8.? on 64 bit linux Ubuntu.  Behaviour is
 consistent with clang++-libc++, but inconsistent with MSVC.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10809>
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