collate, collate_byname

collate_bynamecollatelocale::facet 

• Summary
• Data Type and Member Function Indexes
• Synopsis
• Description
• Interface
• Types
• Constructors
• Destructors
• Facet ID
• Public Member Functions
• Protected Member Functions
• Example
• See Also

A string collation, comparison, and hashing facet.

Data Types

char_type id string_type

Member Functions
compare() do_compare() do_hash() do_transform() hash() transform()

#include <locale>
template <class charT> class collate;
template <class charT> class collate_byname;

The collate and collate_byname facets allow for string collation, comparison, and hashing. Use the collate facet for the "C" locale, and use the collate_byname for named locales.

template <class 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*, const charT*,
              const charT*, const charT*) const;
  string_type transform(const charT*, const charT*) const;
  long hash(const charT*, const charT*) const;
  static locale::id id;
protected:
  ~collate();  // virtual
  virtual int do_compare(const charT*, const charT*,
                         const charT*, const charT*) const;
  virtual string_type do_transform(const charT*, 
                              const charT*) const;
  virtual long do_hash (const charT*, const charT*) const;
};

template <class charT>
class collate_byname : public collate<charT> {
public:
  typedef basic_string<charT> string_type;
  explicit collate_byname(const char*, size_t = 0);
protected:
  ~collate_byname();  // virtual
  virtual int do_compare(const charT*, const charT*,
                         const charT*, const charT*) const;
  virtual string_type do_transform(const charT*, 
                              const charT*) const;
  virtual long do_hash(const charT*, const charT*) const;
};

char_type

Type of character the facet is instantiated on.

string_type

Type of character string returned by member functions.

explicit collate(size_t refs = 0) 

Construct a collate facet. If the refs argument is 0, destruction of the object is delegated to the locale, or locales, containing it. This allows the user to ignore lifetime management issues. On the other hand, if refs is 1, the object must be explicitly deleted: the locale does not do so.

explicit collate_byname(const char* name, size_t refs = 0); 

Construct a collate_byname facet. Use the named locale specified by the name argument. The refs argument serves the same purpose as it does for the collate constructor.

~collate();  // virtual and protected
~collate_byname();  // virtual and protected

Destroy the facet.

static locale::id id; 

Unique identifier for this type of facet.

The public members of the collate facet include an interface to protected members. Each public member xxx has a corresponding virtual protected member do_xxx. All work is delegated to these protected members. For instance, the long version of the public compare function simply calls its protected cousin do_compare.

int 
compare(const charT* low1, const charT* high1,
        const charT* low2, const charT* high2) const; 
long 
hash(const charT* low, const charT* high) const; 
string_type 
transform(const charT* low, const charT* high) const; 

Each of these public member functions xxx simply call the corresponding protected do_xxx function.

virtual int    
do_compare(const charT* low1, const charT* high1,
           const charT* low2, const charT* high2) const; 

Returns 1 if the character string represented by the range [low1,high1) is greater than the character string represented by the range [low2,high2), -1 if first string is less than the second, or 0 if the two are equal. The default instantiations, collate<char> and collate<wchar_t>, perform a lexicographical comparison.

virtual long   
do_hash( const charT* low, const charT* high) 

Generates a hash value from a string defined by the range of characters [low,high). Given two strings that compare equal (in other words, do_compare returns 0), do_hash returns an integer value that is the same for both strings. For differing strings the probability that the return value is equal is approximately:

1.0/numeric_limits<unsigned long>::max()

virtual string_type 
do_transform(const charT* low, const charT* high) const; 

Returns a string that yields the same result in a lexicographical comparison with another string returned from transform as does the do_compare function applied to the original strings. In other words, the result of applying a lexicographical comparison to two strings returned from transform is the same as applying do_compare to the original strings passed to transform.

//
// collate.cpp
//
#include <iostream>

int main ()
{
  using namespace std;
  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;
  return 0;
}

locale, facets, ctype