Question

I’m trying to compile a reverse iterator but my attempts to do so give a horrid mess. The minimal example of the code is…

#include <iostream>
#include <vector>
#include <algorithm>

class frag {
    public:
        void print (void) const;
    private:
        std::vector<int> a;
};

void frag::print (void) const
{
    for (std::vector<int>::reverse_iterator iter = a.begin ();
         iter                                   != a.end ();
         ++iter) {
        std::cout << *iter << std::endl;
    }
}

and attempting to compile it produces the following…

In file included from /usr/include/c++/4.4/bits/stl_algobase.h:69,
             from /usr/include/c++/4.4/bits/char_traits.h:41,
             from /usr/include/c++/4.4/ios:41,
             from /usr/include/c++/4.4/ostream:40,
             from /usr/include/c++/4.4/iostream:40,
             from frag.cpp:1:
/usr/include/c++/4.4/bits/stl_iterator.h: In constructor ‘std::reverse_iterator<_Iterator>::reverse_iterator(const std::reverse_iterator<_Iter>&) [with _Iter = __gnu_cxx::__normal_iterator<const int*, std::vector<int, std::allocator<int> > >, _Iterator = __gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >]’:
frag.cpp:14:   instantiated from here
/usr/include/c++/4.4/bits/stl_iterator.h:134: error: no matching function for call to ‘__gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >::__normal_iterator(__gnu_cxx::__normal_iterator<const int*, std::vector<int, std::allocator<int> > >)’
/usr/include/c++/4.4/bits/stl_iterator.h:686: note: candidates are: __gnu_cxx::__normal_iterator<_Iterator, _Container>::__normal_iterator(const _Iterator&) [with _Iterator = int*, _Container = std::vector<int, std::allocator<int> >]
/usr/include/c++/4.4/bits/stl_iterator.h:683: note:                 __gnu_cxx::__normal_iterator<_Iterator, _Container>::__normal_iterator() [with _Iterator = int*, _Container = std::vector<int, std::allocator<int> >]
/usr/include/c++/4.4/bits/stl_iterator.h:669: note:                 __gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >::__normal_iterator(const __gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >&)

There was a question on this subject yesterday but I don’t think this is the same as it isn’t a template. If a vector is declared in a similar way locally it is quite happy. (g++ on Ubuntu 10.4).

Anyone know what I should do?

Answer 1

You need to use const_reverse_iterator (print is a const function so a is const) and a.rbegin() and a.rend() rather than begin() and end().