problem with iterator (map iterator)

From:

Jim Anderson <jjanderson52000@yahoo.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 10 Jan 2014 08:52:20 -0500

Message-ID:

<laoulm$sju$1@speranza.aioe.org>

I'm writing a small program that will use a map (i.e. map<string,int>).
it has been a while since I have written in c++, so I found an example
on the internet and modified it for my own use. But when I try to
compile my program, I get a compile error.

The code looks ok to me, so I did a search on the internet to see if
others had the same problem. I found 3 or 4 examples, but the solutions
were all related to using an iterator, when infact a const_iterator
should be used. That is not the cause of my problem, as near as I can tell.

I have reduced my code to a simple example:

   1
   2 #include <iostream>
   3 #include <map>
   4 #include <string>
   5
   6 using namespace std;
   7
   8 int main()
   9 {
  10 map<string, int> totals;
  11
  12 totals.insert(std::pair<string,int>("NJ",10));
  13 totals.insert(std::pair<string,int>("NY",20));
  14 totals.insert(std::pair<string,int>("PA",30));
  15 totals.insert(std::pair<string,int>("CT",40));
  16
  17 map<int,string>::iterator iter;
  18 for(iter = totals.begin(); iter != totals.end(); ++iter) {
  19 cout << (*iter).first << ": " << (*iter).second << endl;
  20 }
  21 }

I'm using the GNU compiler g++ version 4.4.5 on crunchbang linux. The
compile error messages are:

   1 g++ -g -Wall -I/home/jja/bfs/include -DLINUX -c problem.cc
   2 problem.cc: In function ?int main()?:
   3 problem.cc:18: error: no match for ?operator=? in ?iter =
totals.std::map<_Key, _Tp, _Compare, _Alloc>::begin [ with _Key =
std::basic_string<char, std::char_traits<char>, std::allocator<char> >,
_Tp = int, _Compare = std:: less<std::basic_string<char,
std::char_traits<char>, std::allocator<char> > >, _Alloc =
std::allocator<std::pai r<const std::basic_string<char,
std::char_traits<char>, std::allocator<char> >, int> >]()?
   4 /usr/include/c++/4.4/bits/stl_tree.h:154: note: candidates are:
std::_Rb_tree_iterator<std::pair<const int, std ::basic_string<char,
std::char_traits<char>, std::allocator<char> > > >&
std::_Rb_tree_iterator<std::pair<const int, std::basic_string<char,
std::char_traits<char>, std::allocator<char> > > >::operator=(const
std::_Rb_tree _iterator<std::pair<const int, std::basic_string<char,
std::char_traits<char>, std::allocator<char> > > >&)
   5 problem.cc:18: error: no match for ?operator!=? in ?iter !=
totals.std::map<_Key, _Tp, _Compare, _Alloc>::end [ with _Key =
std::basic_string<char, std::char_traits<char>, std::allocator<char> >,
_Tp = int, _Compare = std:: less<std::basic_string<char,
std::char_traits<char>, std::allocator<char> > >, _Alloc =
std::allocator<std::pai r<const std::basic_string<char,
std::char_traits<char>, std::allocator<char> >, int> >]()?
   6 /usr/include/c++/4.4/bits/stl_tree.h:216: note: candidates are:
bool std::_Rb_tree_iterator<_Tp>::operator!=(co nst
std::_Rb_tree_iterator<_Tp>&) const [with _Tp = std::pair<const int,
std::basic_string<char, std::char_trai ts<char>, std::allocator<char>
> >]
   7 make: *** [problem.o] Error 1

Can anyone help explain the compile errors/

Jim Anderson