error on std::operator==(istream_iterator, istream_iterator)

• Key: STDCXX-321
• Type: Bug
• Status: Closed
• Resolution: Fixed
• Priority: Major
• Assignee: Martin Sebor
• Reporter: Martin Sebor
• Component/s: 24. Iterators
• Affects Version/s: 4.1.2, 4.1.3, 4.1.4, 4.2.0
• Fix Version/s: 4.2.1

Description

The well-formed program below fails to compile with both EDG eccp 3.8 and gcc 4.1.0 (I didn't try others but it's likely a bug in the library)

$ cat t.cpp && make t
#include <iterator>

int main ()
{
    std::istream_iterator<char, char> i;
    (void)(i == i);
}

eccp -c -I/build/sebor/dev/stdlib/include/ansi -D_RWSTDDEBUG    -D_RWSTD_USE_CONFIG -I/build/sebor/dev/stdlib/include -I/build/sebor/eccp-3.8-11s/include -I/build/sebor/dev/stdlib/include/ansi -I/build/sebor/PlumHall/lvs06a/conform -I/build/sebor/PlumHall/lvs06a/dst.3  -A -x --template_directory=/build/sebor/eccp-3.8-11s/lib -g  --display_error_number --remarks --diag_suppress 193,236,340,401,261,479,487,678,679,815 --diag_suppress 177,381,191,68,550,611,997,549   t.cpp
"/build/sebor/dev/stdlib/include/rw/_streamiter.h", line 124: error #349: no
          operator "!" matches these operands
            operand types are: ! std::basic_istream<char,
                      std::char_traits<char>>
      return (__x._C_strm && !!*__x._C_strm) == (__y._C_strm && !!*__y._C_strm);
                              ^
          detected during instantiation of "bool std::operator==(const
                    std::istream_iterator<_TypeT, _CharT, _Traits, _Distance>
                    &, const std::istream_iterator<_TypeT, _CharT, _Traits,
                    _Distance> &) [with _TypeT=char, _CharT=char,
                    _Traits=std::char_traits<char>, _Distance=int]" at line 6
                    of "t.cpp"

"/build/sebor/dev/stdlib/include/rw/_streamiter.h", line 124: error #349: no
          operator "!" matches these operands
            operand types are: ! std::basic_istream<char,
                      std::char_traits<char>>
      return (__x._C_strm && !!*__x._C_strm) == (__y._C_strm && !!*__y._C_strm);
                                                                 ^
          detected during instantiation of "bool std::operator==(const
                    std::istream_iterator<_TypeT, _CharT, _Traits, _Distance>
                    &, const std::istream_iterator<_TypeT, _CharT, _Traits,
                    _Distance> &) [with _TypeT=char, _CharT=char,
                    _Traits=std::char_traits<char>, _Distance=int]" at line 6
                    of "t.cpp"

2 errors detected in the compilation of "t.cpp".
make: *** [t.o] Error 2

Comments

[Martin Sebor]

Scheduled for 4.2.1.

[Martin Sebor]

This affects all released versions.

[Farid Zaripov]

The problem is that operator==(istream_iterator<>&, istream_iterator<>&) calls basic_istream::operator!(), but basic_istream::operator!() is defined in <istream> header file.

So <istream> should be included in rw/_streamiter.h.

The similar problem in STDCXX-375.

[Martin Sebor]

I'm not sure #including all of <istream> in <iterator> is a good idea. But see STDCXX-645.

[Farid Zaripov]

We could change the operator==(istream_iterator<>&, istream_iterator<>&) to just compare the pointers _C_strm, but anyway the basic_istream::operator!(), is used in istream_iterator::operator++() and the following example also would fail:

#include <iterator>

int main ()
{
    std::istream_iterator<char, char> i;
    ++i;
    i++;
}

[Farid Zaripov]

The Dinkumware STL doesn't #includes <istream> in <iterator> and the example with incrementing of the iterator is also fail to compile (the example with operator==() doesn't fail because operator==() implementation compares the pointers only).

The STLport #includes basic_istream definitions before definitions of the istream_iterator.
The SGI STL from gcc also #includes <istream> in <iterator>.

[Martin Sebor]

Disabled formatting.

[Martin Sebor]

I've been working on STDCXX-645 and I expect to have a solution for the equality operator. I don't think your test case with the increment operator is solvable without #including <istream> in <iterator> which we probably don't want to do because of all the baggage that <istream> brings in with it (locale, string, etc.)

Fundamentally, this is LWG issue 343.

[Martin Sebor]

Reassigning to self since this depends on STDCXX-645 that I've been working on.

[Martin Sebor]

The original issue has been fixed – see the patch committed in r618883 for STDCXX-645.
The original test case has been committed to our regression test suite in r619099.

The test case from Farid's comment above still doesn't compile but since that one has undefined behavior I'm not concerned.

[Martin Sebor]

Closing as fixed.

[Farid Zaripov]

Merged in 4.2.x branch thus: http://svn.apache.org/viewvc?view=rev&revision=648752