Re: compilation error with const_reverse_iterator

From:
Barry <dhb2000@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Thu, 04 Oct 2007 14:23:03 +0800
Message-ID:
<fe24hf$5ka$1@news.cn99.com>
subramanian100in@yahoo.com, India wrote:

Consider the following program:

#include <iostream>
#include <map>
#include <string>
#include <utility>
#include <algorithm>

using namespace std;

int main()
{
map<string, int> si;

string word;

while (cin >> word)
    ++si[word];

multimap<int, string> is;

for (map<string, int>::const_iterator i = si.begin(); i != si.end(); +
+i)
    is.insert(make_pair(i->second, i->first));

for (multimap<int, string>::const_reverse_iterator r = is.rbegin(); r !
= is.rend(); ++r)
    cout << r->second << " " << r->first << endl;

return 0;
}

Under g++, I get compilation error for the line

for (multimap<int, string>::const_reverse_iterator r = is.rbegin(); r !
= is.rend(); ++r)


Ah,
As you declare
 >multimap<int, string> is;
then /is.rend()/ and /is.rbegin()/ are both reverse_iterators
r = is.begin(), compiles as is convertible from reverse_iterator to
const_reverse_iterator.

Threre are no /operator !=/ or /operator ==/ between the two types.

so you can simply choose reverse_iterator for r

The actual error message is

error: no match for 'operator!=' in 'r != std::multimap<_Key, _Tp,
_Compare, _Alloc>::rend() [with _Key = int, _Tp = std::string,
_Compare = std::less<int>, _Alloc = std::allocator<std::pair<const
int, std::string> >]()'

However this program compiles fine under VC++ 2005 Express Edition.


I think this is an extension from VC.

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