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]

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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; }; }
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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]

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

30.4.8.2.3 Virtual functions [locale.messages.virtuals]

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catalog do_open(const string& name, const locale& loc) const;
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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().
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Returns a value less than 0 if no such catalog can be opened.
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Remarks: The locale argument loc is used for character set code conversion when retrieving messages, if needed.
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string_type do_get(catalog cat, int set, int msgid, const string_type& dfault) const;
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Preconditions: cat is a catalog obtained from open() and not yet closed.
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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.
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void do_close(catalog cat) const;
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Preconditions: cat is a catalog obtained from open() and not yet closed.
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Effects: Releases unspecified resources associated with cat.
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Remarks: The limit on such resources, if any, is implementation-defined.