Strange bug with iterators

From:
Juha Nieminen <nospam@thanks.invalid>
Newsgroups:
comp.lang.c++
Date:
Fri, 18 May 2012 18:10:56 +0000 (UTC)
Message-ID:
<jp63bg$h1m$1@speranza.aioe.org>
I have this piece of (C++11) code:

//----------------------------------------------------------------------
#include <iterator>

template<typename Iter_t>
struct RangeWrapper
{
    Iter_t mBegin, mEnd;
    RangeWrapper(Iter_t b, Iter_t e): mBegin(b), mEnd(e) {}
    Iter_t begin() { return mBegin; }
    Iter_t end() { return mEnd; }
};

template<typename Container_t>
RangeWrapper<typename Container_t::reverse_iterator>
revRange(Container_t container)
{
    return { container.rbegin(), container.rend() };
}

#include <vector>
#include <iostream>

int main()
{
    std::vector<int> v = { 1, 3, 5, 7, 9 };

    for(int i: revRange(v)) std::cout << " " << i;
    std::cout << "\n";
}
//----------------------------------------------------------------------

For some reason it does not work properly when compiled with gcc 4.6.3.
It prints the first numbers ok, but then it starts printing zeros.

If I compile with -D_GLIBCXX_DEBUG I get a strange runtime error:

/usr/include/c++/4.6/debug/safe_iterator.h:142:error: attempt to copy-
    construct an iterator from a singular iterator.

I don't understand what that means.

When run with gdb, the backtrace indicates that the error seems to
happen in RangeWrapper::begin().

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