C++ Cookbook

13.5. Sorting Localized Strings

Problem

You have a sequence of strings that contain non-ASCII characters, and you need to sort according to local convention.

Solution

The locale class has built-in support for comparing characters in a given locale by overriding operator. You can use an instance of the locale class as your comparison functor when you call any standard function that takes a functor for comparison. (See Example 13-8.)

Example 13-8. Locale-specific sorting

#include <iostream>
#include <locale>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

bool localeLessThan (const string& s1, const string& s2) {

   const collate<char>& col =
     use_facet<collate<char> >(locale()); // Use the global locale

   const char* pb1 = s1.data();
   const char* pb2 = s2.data();

   return (col.compare(pb1, pb1 + s1.size(),
                       pb2, pb2 + s2.size()) < 0);
}

int main() {

   // Create two strings, one with a German character
   string s1 = "diät";
   string s2 = "dich";

   vector<string> v;
   v.push_back(s1);
   v.push_back(s2);

   // Sort without giving a locale, which will sort according to the
   // current global locale's rules.
   sort(v.begin(), v.end());
   for (vector<string>::const_iterator p = v.begin();
        p != v.end(); ++p)
      cout << *p << endl;

   // Set the global locale to German, and then sort
   locale::global(locale("german"));
   sort(v.begin(), v.end(), localeLessThan);
   for (vector<string>::const_iterator p = v.begin();
        p != v.end(); ++p)
      cout << *p << endl;
}

The first sort follows ASCII sorting convention, ...