22 Localization library [localization]

22.4 Standard locale categories [locale.categories]

22.4.7 The message retrieval category [category.messages]

22.4.7.1 Class template messages [locale.messages]

namespace std {
  class messages_base {
  public:
    using catalog = unspecified signed integer type;
  };

  template <class charT>
  class messages : public locale::facet, public messages_base {
  public:
    using char_type   = charT;
    using string_type = basic_string<charT>;

    explicit messages(size_t refs = 0);

    catalog open(const basic_string<char>& fn, const locale&) const;
    string_type get(catalog c, int set, int msgid,
                     const string_type& dfault) const;
    void close(catalog c) const;

    static locale::id id;

  protected:
    ~messages();
    virtual catalog do_open(const basic_string<char>&, const locale&) const;
    virtual string_type do_get(catalog, int set, int msgid,
                               const string_type& dfault) const;
    virtual void do_close(catalog) const;
  };
}
1

Values of type messages_base::catalog usable as arguments to members get and close can be obtained only by calling member open.

22.4.7.1.1 messages members [locale.messages.members]

catalog open(const basic_string<char>& name, const locale& loc) const;

1

Returns: do_open(name, loc).

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

2

Returns: do_get(cat, set, msgid, dfault).

void close(catalog cat) const;

3

Effects: Calls do_close(cat).

22.4.7.1.2 messages virtual functions [locale.messages.virtuals]

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

1

Returns: A value that may be passed to get() to retrieve a message from the message catalog identified by the string name according to an implementation-defined mapping. The result can be used until it is passed to close().

2

Returns a value less than 0 if no such catalog can be opened.

3

Remarks: The locale argument loc is used for character set code conversion when retrieving messages, if needed.

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

4

Requires: cat shall be a catalog obtained from open() and not yet closed.

5

Returns: A message identified by arguments set, msgid, and dfault, according to an implementation-defined mapping. If no such message can be found, returns dfault.

void do_close(catalog cat) const;

6

Requires: cat shall be a catalog obtained from open() and not yet closed.

7

Effects: Releases unspecified resources associated with cat.

8

Remarks: The limit on such resources, if any, is implementation-defined.