C++ In a Nutshell

Name

collate class template — Facet for comparing strings in collation order

Synopsis

template <typename charT>
class collate : public locale::facet
{
public:
  typedef charT char_type;
  typedef basic_string<charT> string_type;
  explicit collate(size_t refs = 0);
  int compare(const charT* low1, const charT* high1, const charT* low2,
              const charT* high2) const;
  string_type transform(const charT* low, const charT* high) const;
  long hash(const charT* low, const charT* high) const;
  static locale::id id;
protected:
  virtual ~collate(  );
  virtual int do_compare(const charT* low1, const charT* high1, 
                         const charT* low2, const charT* high2) const;
  virtual string_type do_transform (const charT* low, const charT* high) const;
  virtual long do_hash (const charT* low, const charT* high) const;
};

The collate class template is a facet used to compare strings. In some locales, the collation order of characters is not the same as the numerical order of their encodings, and some characters might be logically equivalent even if they have different encodings.

You can use a locale object as a comparator for algorithms that need a comparison function; the locale’s operator( ) function uses the collate facet to perform the comparison.

The standard mandates the collate<char> and collate<wchar_t> instantiations, which perform lexicographical (element-wise, numerical) comparison. See lexicographical_compare in <algorithm> earlier in this chapter.

As with other facets, the public members call virtual, protected members ...