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Date: Wed, 07 Sep 2005 17:03:00 -0000
From: "afra at cs dot stanford dot edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20050907170304.23767.afra@cs.stanford.edu>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug c++/23767] New: std::vector iterator implementation wrong
X-Bugzilla-Reason: CC
X-SW-Source: 2005-09/txt/msg00832.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

The following code does not compile.  According to the compiler, 
't' is overloaded ambiguously.

#include <vector>

struct T {
  typedef std::vector<int> Vector;
  typedef Vector::iterator iterator;
  typedef Vector::const_iterator const_iterator;

  int t( iterator f)             { return *f; }
  int t( const_iterator f) const { return *f; }
};

int main(int, char*[])
{
  std::vector<int> v;
  T t;
  T::const_iterator i = v.begin();

  t.t(i);

  return 0;

}

We've seen this on gcc 3.2.2., 3.4.3, 4.0.1.  Basically, the
const_iterator matches both the iterator and the const_iterator at function
resolution time.  This seems to stem from the implementation of iterator in
std::vector using __normal_iterator.  There is a template copy constructor that
appears to allow this illegal conversion.

Error on:  gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)
----------
test.cc: In function int main(int, char**):
test.cc:18: error: ISO C++ says that these are ambiguous, even though
the
worst conversion for the first is better than the worst conversion for
the
second:
test.cc:10: note: candidate 1: int
T::t(__gnu_cxx::__normal_iterator<const
int*, std::vector<int, std::allocator<int> > >) const
test.cc:9: note: candidate 2: int
T::t(__gnu_cxx::__normal_iterator<int*,
std::vector<int, std::allocator<int> > >)

-- 
           Summary: std::vector iterator implementation wrong
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: afra at cs dot stanford dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23767