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messages, messages_byname

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messages, messages_byname

messages_base messages_bynamemessages locale::facet


Messaging facets.

Data Type and Member Function Indexes
(exclusive of constructors and destructors)


class messages_base;

template <class charT> class messages;


messages provides access to a localized messaging facility. The messages facet provides facilities based on the "C" locale, while the messages_byname facet provides the same facilities for named locales.

The messages_base class provides a catalog type for use by the derived messages and messages_byname classes.

Note that the default messages facet uses catopen, catclose, etc., to implement the message database. If your platform does not support these then you'll need to imbue your own messages facet by implementing whatever database is available.


class messages_base {
  typedef int catalog;

template <class charT>
class messages : public locale::facet, public messages_base {
  typedef charT char_type;
  typedef basic_string<charT> string_type;
  explicit messages(size_t = 0);
  catalog open(const basic_string<char>&, const locale&) const;
  string_type  get(catalog, int, int,
                   const string_type&) const;
  void    close(catalog) const;
  static locale::id id;
  ~messages();  // virtual
  virtual catalog do_open(const basic_string<char>&, 
                          const locale&) const;
  virtual string_type  do_get(catalog, int, int,
                              const string_type&) const;
  virtual void    do_close(catalog) const;

class messages_byname : public messages<charT> {
  explicit messages_byname(const char*, size_t = 0);
  ~messages_byname();  // virtual
  virtual catalog do_open(const basic_string<char>&, 
                          const locale&) const;
virtual string_type  do_get(catalog, int, int,
                            const string_type&) const;
  virtual void    do_close(catalog) const;



    Type of character the facet is instantiated on.


    Type of character string returned by member functions.

Constructors and Destructors

explicit messages(size_t refs = 0)

    Construct a messages facet. If the refs argument is 0 then 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 then the object must be explicitly deleted: the locale will not do so. In this case, the object can be maintained across the lifetime of multiple locales.

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

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

~messages();  // virtual and protected

    Destroy the facet

Facet ID

static locale::id id;

    Unique identifier for this type of facet.

Public Member Functions

The public members of the messages facet provide 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 open function simply calls its protected cousin do_open.

close(catalog c) const;

get(catalog c, int set, int msgid, 
    const string_type& dfault) const;

open(const basic_string<char>& fn, const locale&) const;

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

Protected Member Functions

virtual void    
do_close(catalog cat) const;

    Closes the catalog. The cat argument must have been obtained by a call to open().

virtual string_type  
do_get(catalog cat, int set, int msgid, 
       const string_type& dfault) const;

    Retrieves a specific message. Returns the message identified by cat, set, msgid, and dfault. cat must have been obtained by a previous call to open() and this function must not be called with a cat that has had close() called on yet after the last call to open(). In other words, the catalog must have been opened and not yet closed.

virtual catalog 
do_open(const basic_string<char>& name, const locale&) const;

    Opens a message catalog. Returns a catalog identifier that can be passed to the get() function in order to access specific messages. Returns -1 if the catalog name specified in the name argument is invalid. The loc argument will be used for codeset conversion if necessary.


// messages.cpp
#include <string>
#include <iostream>

int main ()
  using namespace std;

  locale loc;

  // Get a reference to the messages<char> facet
  const messages<char>& mess = 
    use_facet<messages<char> >(loc);

  // Open a catalog and try to grab
  // both some valid messages, and an invalid message
  string def("Message Not Found");
  messages<char>::catalog cat =
  if (cat != -1)
    string msg0 = mess.get(cat,1,1,def);
    string msg1 = mess.get(cat,1,2,def);
    string msg2 = mess.get(cat,1,6,def); // invalid msg #
    string msg3 = mess.get(cat,2,1,def);

    cout << msg0 << endl << msg1 << endl
         << msg2 << endl << msg3 << endl;
    cout << "Unable to open message catalog" << endl;

  return 0;

See Also

locale, facets

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