Re: reverse_iterator and const_reverse_iterator

From:

Jess <wdfcj@hotmail.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 18 Jun 2007 02:43:47 -0700

Message-ID:

<1182159827.726657.132470@z28g2000prd.googlegroups.com>

On Jun 18, 2:35 pm, "V.R. Marinov" <v.r.mari...@gmail.com> wrote:

Jess :

On Jun 18, 4:17 am, Pete Becker <p...@versatilecoding.com> wrote:

Roland Pibinger wrote:

On Sun, 17 Jun 2007 06:45:56 -0700, Jess wrote:

I think the two reverse_iterators are the same, except that the const_
version doesn't allow me to change the value pointed to by the
iterators. However, I have a program that works for reverse_iterator
but not const_reverse_iterator:

for(vector<int>::const_reverse_iterator i = v.rbegin(); i != v.rend();
++i)
cout << (*i) << endl;

This one fails, with error

no match for 'operator!=' in 'i != std::vector<_Tp, _Alloc>::rend()
[with _Tp = int, _Alloc = std::allocator<int>]()'

I guess your compiler cannot distinguish between the const and the
non-const rend(). Try:

Seems like it does distinguish between them, and calls the non-const
version on a non-const vector. The problem arises from comparing a
const_iterator to a plain iterator.

for(vector<int>::const_reverse_iterator i = v.rbegin();
i != ((const std::vector<int>) v).rend();

i != ((const std::vector<int>&) v).rend();

That's a minor typo, but critical. As written, it copies the vector,
creating an iterator that points into the copy rather than the original.

Thanks, I tried both methods, but neither worked... I think I only
need to cast a non-const "v" to a const "v", hence I tried

for(vector<int>::const_reverse_iterator i = v.rbegin(); i !=
(static_cast<const vector<int> >)v.rend(); ++i)
cout << (*i) << endl;

Unfortunately, it failed as well

It looks like you are using the wrong syntax. It should be.

i != static_cast<const vector<int>& >(v).rend()

Thanks. I tried but it still doesn't work. Here's the entire
program.

#include<vector>
#include<string>
#include<iterator>
#include<iostream>
using namespace std;

int main(){
  vector<int> v;
  for(int i = 0; i != 10; ++i)
    v.push_back(i);

  for(vector<int>::const_reverse_iterator i = v.rbegin(); i !=
static_cast<vector<int>& >(v).rend(); ++i)
    cout << (*i) << endl;
  return 0;
}

The error message was

no match for 'operator!=' in 'i != std::vector<_Tp, _Alloc>::rend()
[with _Tp = int, _Alloc = std::allocator<int>]()'

Jess