30 Localization library [localization]

30.4 Standard locale categories [locale.categories]

30.4.8 The message retrieval category [category.messages]

30.4.8.2 Class template messages [locale.messages]

30.4.8.2.1 General [locale.messages.general]

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 string& 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 string&, const locale&) const; virtual string_type do_get(catalog, int set, int msgid, const string_type& dfault) const; virtual void do_close(catalog) const; }; }
Values of type messages_­base​::​catalog usable as arguments to members get and close can be obtained only by calling member open.

30.4.8.2.2 Members [locale.messages.members]

catalog open(const string& name, const locale& loc) const;
Returns: do_­open(name, loc).
string_type get(catalog cat, int set, int msgid, const string_type& dfault) const;
Returns: do_­get(cat, set, msgid, dfault).
void close(catalog cat) const;
Effects: Calls do_­close(cat).

30.4.8.2.3 Virtual functions [locale.messages.virtuals]

catalog do_open(const string& name, const locale& loc) const;
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().
Returns a value less than 0 if no such catalog can be opened.
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;
Preconditions: cat is a catalog obtained from open() and not yet closed.
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;
Preconditions: cat is a catalog obtained from open() and not yet closed.
Effects: Releases unspecified resources associated with cat.
Remarks: The limit on such resources, if any, is implementation-defined.