Case insensitive set of strings

Hi,

I want a const static std::set of strings which is case insensitive
for the values.

So I have the following which seems to work but something doesnt seem
right about it. Is there a better way or any gotcha's from my code
below.

TIA

Adrian

#include <iostream>
#include <functional>
#include <algorithm>
#include <set>
#include <string>
#include <iterator>

class Test
{
   public:
      void p()
      {
        std::copy(fields.begin(), fields.end(),
std::ostream_iterator<std::string>(std::cout, ","));
        std::cout << std::endl;
      }
   private:
      struct nocase_cmp : public std::binary_function<const
std::string &, const std::string &, bool>
      {
         struct nocase_char_cmp : public std::binary_function<char,
char, bool>
         {
            bool operator()(char a, char b)
            {
               return std::toupper(a) < std::toupper(b);
            }
         };
         bool operator()(const std::string &a, const std::string &b)
         {
            return std::lexicographical_compare(a.begin(), a.end(),
b.begin(), b.end(),
               nocase_char_cmp());
         }
      };

      typedef std::set<std::string, nocase_cmp> Field_names_t;
      static const Field_names_t fields;
};
const char *f[]={
   "string1",
   "string2",
   "string3",
   "STRIng1",
   "string5"};

const Test::Field_names_t Test::fields(f, f+5);

int main(int argc, char *argv[])
{
   Test t;
   t.p();

   return 0;
}