[Bug libstdc++/38678] New: istream::read() calls streambuf::xsgetn()

[Bug libstdc++/38678] New: istream::read() calls streambuf::xsgetn()

[sebor at roguewave dot com]

As mentioned in bug 38476, [lib.istream], p2 specifies that:

  Both [formatted and unformatted] input functions are described as if
  they obtain (or extract) input characters by calling rdbuf()->sbumpc()
  or rdbuf()->sgetc(). They may use other public members of istream.

sgetc() is required to return the result of underflow() and sbumpc() is
required to return the result of uflow(). An implementation of
istream::read() may call streambuf::xsgetn() but it must do so in a way
that achieves the "as if" effect described above. Notably, it must avoid
calling an xsgetn() overridden in a derived class. The test case below
shows that the gcc implementation fails to do so.

$ cat z.cpp && g++ z.cpp && ./a.out 
#include <cassert>
#include <istream>
#include <streambuf>

int main ()
{
    static int x = '0';

    struct: std::streambuf {
        char c;

        int_type underflow () {
            c = x++;
            setg (&c, &c, &c + 1);
            return c;
        }

        std::streamsize xsgetn (char*, std::streamsize) {
            assert (!"xsgetn should not be called");
            return 0;
        }
    } sb;

    std::istream in (&sb);

    char s [4] = "";

    in.read (s, sizeof s);

    assert (in.good ());
    assert (sizeof s == in.gcount ());
    assert ('0' == s [0] && '1' == s [1] && '2' == s [2] && '3' == s [3]);
}
a.out: z.cpp:19: virtual std::streamsize main()::<anonymous
struct>::xsgetn(char*, std::streamsize): Assertion `!"xsgetn should not be
called"' failed.
Aborted


-- 
           Summary: istream::read() calls streambuf::xsgetn()
           Product: gcc
           Version: 4.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sebor at roguewave dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] istream::read() calls streambuf::xsgetn()

[paolo dot carlini at oracle dot com]

------- Comment #1 from paolo dot carlini at oracle dot com  2008-12-31 00:06 -------
Ok, thanks.


-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |paolo dot carlini at oracle
                   |dot org                     |dot com
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-12-31 00:06:28
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] istream::read() calls streambuf::sgetn()

[paolo dot carlini at oracle dot com]

------- Comment #2 from paolo dot carlini at oracle dot com  2008-12-31 17:44 -------
Note, istream::read currently calls streambuf::sgetn *not* streambuf::xsgetn,
because the latter is protected and in general would be incorrect calling it
anyway.


-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|istream::read() calls       |istream::read() calls
                   |streambuf::xsgetn()         |streambuf::sgetn()


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] istream::read() calls streambuf::sgetn()

[paolo at gcc dot gnu dot org]

------- Comment #3 from paolo at gcc dot gnu dot org  2009-01-01 10:09 -------
Subject: Bug 38678

Author: paolo
Date: Thu Jan  1 10:08:31 2009
New Revision: 142994

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=142994
Log:
2009-01-01  Paolo Carlini  <paolo.carlini@oracle.com>

        PR libstdc++/38678
        * include/std/istream (basic_istream<>::_M_read): New.
        * include/bits/istream.tcc (basic_istream<>::_M_read): Define.
        (basic_istream<>::read, basic_istream<>::readsome): Use it.
        * include/std/ostream (basic_ostream<>::_M_write_): New.
        (basic_ostream<>::_M_write): Adjust.
        * include/bits/ostream.tcc (basic_ostream<>::_M_write_): Define.
        * testsuite/27_io/basic_istream/read/char/38678.cc: New.
        * testsuite/27_io/basic_istream/read/wchar_t/38678.cc: Likewise.
        * testsuite/27_io/basic_ostream/write/char/38678.cc: Likewise.
        * testsuite/27_io/basic_ostream/write/wchar_t/38678.cc: Likewise.

Added:
    trunk/libstdc++-v3/testsuite/27_io/basic_istream/read/char/38678.cc
    trunk/libstdc++-v3/testsuite/27_io/basic_istream/read/wchar_t/38678.cc
    trunk/libstdc++-v3/testsuite/27_io/basic_ostream/write/char/38678.cc
    trunk/libstdc++-v3/testsuite/27_io/basic_ostream/write/wchar_t/38678.cc
Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/bits/istream.tcc
    trunk/libstdc++-v3/include/bits/ostream.tcc
    trunk/libstdc++-v3/include/std/istream
    trunk/libstdc++-v3/include/std/ostream


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] istream::read() calls streambuf::sgetn()

[paolo dot carlini at oracle dot com]

------- Comment #4 from paolo dot carlini at oracle dot com  2009-01-01 10:10 -------
Fixed for 4.4.0.


-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[paolo dot carlini at oracle dot com]

-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |SUSPENDED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[paolo dot carlini at oracle dot com]

------- Comment #5 from paolo dot carlini at oracle dot com  2009-01-03 22:37 -------
Changes reverted for now, consistently with the discussion:

  http://gcc.gnu.org/ml/gcc-patches/2009-01/msg00004.html

Waiting for the resolution of a new DR (# to be added Summary).


-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |
            Summary|istream::read() calls       |[DR XXX] istream::read()
                   |streambuf::sgetn()          |calls streambuf::sgetn()


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.0                       |4.4.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.1                       |4.4.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.2                       |4.4.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.3                       |4.4.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.4                       |4.4.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
MSVC and libc++ both behave the same as libstdc++, calling rdbuf()->sgetn():

https://github.com/microsoft/STL/blob/e36ee6c2b9bc6f5b1f70776c18cf5d3a93a69798/stl/inc/istream#L522

https://github.com/llvm/llvm-project/blob/525c25acd364f018b4fa55e941bd702587478b1c/libcxx/include/istream#L897

I think at this point it seems pretty clear we should open a new issue as the
istream counterpart to https://cplusplus.github.io/LWG/issue165 and make the
spec match reality. I can't find an issue on the topic from Martin, so I don't
think it was ever opened.

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.7                       |---

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.6                       |4.4.7

[Bug libstdc++/38678] [DR XXX] istream::read() calls streambuf::sgetn()

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38678

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.4.5                       |4.4.6