Problems with std::copy()

I'm trying to use istream_iterators to read from a file and put words into a set<word>. Word is a class that I've defined that takes a string and removes all non-letters such as punctuation. When I compile I get a really disgusting looking error. Any help? I'm using the newest DJGPP if that helps at all.

Code:

---

set<word> Words;
        set<word>::iterator it=Words.begin();
               
        std::copy(std::istream_iterator<string>(fin),std::istream_iterator<string>(),std::inserter(Words,it));

---

Error:
c:/djgpp/lang/cxx/3.32/bits/stl_function.h: In member function `bool
std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = word]':
c:/djgpp/lang/cxx/3.32/bits/stl_tree.h:1066: instantiated from `std::_Rb_tree_
iterator<_Val, _Val&, _Val*> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _A
lloc>::insert_unique(std::_Rb_tree_iterator<_Val, _Val&, _Val*>, const _Val&) [w
ith _Key = word, _Val = word, _KeyOfValue = std::_Identity<word>, _Compare = std
::less<word>, _Alloc = std::allocator<word>]'
c:/djgpp/lang/cxx/3.32/bits/stl_set.h:160: instantiated from `typename std::_R
b_tree<_Key, _Key, std::_Identity<_Key>, _Compare, _Alloc>::const_iterator std::
set<_Key, _Compare, _Alloc>::insert(typename std::_Rb_tree<_Key, _Key, std::_Ide
ntity<_Key>, _Compare, _Alloc>::const_iterator, const _Key&) [with _Key = word,
_Compare = std::less<word>, _Alloc = std::allocator<word>]'
c:/djgpp/lang/cxx/3.32/bits/stl_iterator.h:524: instantiated from `std::insert
_iterator<_Container>& std::insert_iterator<_Container>::operator=(typena me _Con
tainer::const_reference) [with _Container = std::set<word, std::less<word>, std:
:allocator<word> >]'
c:/djgpp/lang/cxx/3.32/bits/stlalgobase.h:228: instantiated from `_OutputIter
std::__copy(_InputIter, _InputIter, _OutputIter, std::input_iterator_tag) [with
_InputIter = std::istream_iterator<std::string, char, std::char_traits<char>, pt
rdiff_t>, _OutputIter = std::insert_iterator<std::set<word, std::less<word>, std
::allocator<word> > >]'
c:/djgpp/lang/cxx/3.32/bits/stlalgobase.h:260: instantiated from `_OutputIter
std::__copy_aux2(_InputIter, _InputIter, _OutputIter, __false_type) [with _Input
Iter = std::istream_iterator<std::string, char, std::char_traits<char>, ptrdiff_
t>, _OutputIter = std::insert_iterator<std::set<word, std::less<word>, std::allo
cator<word> > >]'
c:/djgpp/lang/cxx/3.32/bits/stlalgobase.h:303: instantiated from `_OutputIter
std::__copy_ni2(_InputIter, _InputIter, _OutputIter, __false_type) [with _InputI
ter = std::istream_iterator<std::string, char, std::char_traits<char>, ptrdiff_t
>, _OutputIter = std::insert_iterator<std::set<word, std::less<word>, std::alloc
ator<word> > >]'
c:/djgpp/lang/cxx/3.32/bits/stlalgobase.h:323: instantiated from `_OutputIter
std::__copy_ni1(_InputIter, _InputIter, _OutputIter, __false_type) [with _InputI
ter = std::istream_iterator<std::string, char, std::char_traits<char>, ptrdiff_t
>, _OutputIter = std::insert_iterator<std::set<word, std::less<word>, std::alloc
ator<word> > >]'
c:/djgpp/lang/cxx/3.32/bits/stlalgobase.h:349: instantiated from `_OutputIter
std::copy(_InputIter, _InputIter, _OutputIter) [with _InputIter = std::istream_i
terator<std::string, char, std::char_traits<char>, ptrdiff_t>, _OutputIter = std
::insert_iterator<std::set<word, std::less<word>, std::allocator<word> > >]'
biblio.cpp:30: instantiated from here
c:/djgpp/lang/cxx/3.32/bits/stl_function.h:197: error: passing `const word' as
`this' argument of `bool word::operator<(word)' discards qualifiers

Oops, I forgot to post word.h. Here's all my code:

biblio.cpp

Code:

---

#include "word.h"
#include <fstream>
#include <iostream>
#include <set>
#include<iterator> /*istream_iterator definition*/
#include<algorithm>
using std::cout;
using std::set;

int main()
{
        std::ifstream fin;
        set<word> Words;
       
        fin.open("Assignment5input.txt");
       
        if(fin.fail())
        {
                cout<<"Error opening Assignment5input.txt";
                return -1;
        }
       
        std::copy(std::istream_iterator<string>(fin),std::istream_iterator<string>(),std::inserter(Words,Words.begin()));
       
        return 0;
}

---

word.h

Code:

---

#include<string>
#include<cctype>
using std::string;

class word
{
        public:
                word(string str1);
                bool operator<(word two);
        private:
                string str;
};

word::word(string str1)
{
        int spot=0;
        char wrd[50];
        for(unsigned i=0;i<str1.length();i++)
        {
                if(isalpha(str1.c_str()[i]))
                {
                        wrd[spot]=tolower(str1.c_str()[i]);
                        spot++;
                }
        }
        str=(string)wrd;
}

bool word::operator<(word two)
{
        int size;
       
        if(str.length()<two.str.length())
                size=str.length();
        else
                size=str.length();
       
        for(int i=0;i<size;i++)
                if(str.c_str()[i]<two.str.c_str()[i])
                        return true;
        return false;
}

---

>passing `const word' as`this' argument of `bool word::operator<(word)' discards qualifiers
Make these two changes:

Code:

---

bool operator<(word two) const;

---

Code:

---

bool word::operator<(word two) const

---

Dude! Thank you VERY much. I really appreciate that! Is there an FAQ or something I could read that would teach me why I need that const? Again, I can't thank you enough. :)

>Is there an FAQ or something I could read that would teach me why I need that const?
If your object is const then any member functions it uses must be const qualified as well. A good book on C++ should explain const correctness.