这个程序怎么理解？co.hash有什么意义？

#include <iostream>
#include <locale>

int main ()
{
#ifndef _RWSTD_NO_NAMESPACE
using namespace std;
#endif

locale loc;
string s1("blue");
string s2("blues");

// Get a reference to the collate<char> facet
const collate<char>& co =
#ifndef _RWSTD_NO_TEMPLATE_ON_RETURN_TYPE
use_facet<collate<char> >(loc);
#else
use_facet(loc,(collate<char>*)0);
#endif

// Compare two strings
cout << co.compare(s1.begin(),s1.end(),
s2.begin(),s2.end()-1) << endl;
cout << co.compare(s1.begin(),s1.end(),
s2.begin(),s2.end()) << endl;

// Retrieve hash values for two strings
cout << co.hash(s1.begin(),s1.end()) << endl;
cout << co.hash(s2.begin(),s2.end()) << endl;

getchar();
return 0;
}
这个是CB里的示例！