std::messages<CharT>::open, std::messages<CharT>::do_open

< cpp‎ | locale‎ | messages
Defined in header <locale>
catalog open( const std::basic_string<char>& name, const std::locale& loc ) const;
virtual catalog do_open( const std::basic_string<char>& name, const std::locale& loc ) const;

1) Public member function, calls the protected virtual member function do_open of the most derived class.

2) Obtains a value of type catalog (inherited from std::messages_base), which can be passed to get() to retrieve messages from the message catalog named by name. This value is usable until passed to close().


name - name of the message catalog to open
loc - a locale object that provides additional facets that may be required to read messages from the catalog, such as std::codecvt to perform wide/multibyte conversions

Return value

The non-negative value of type catalog that can be used with get() and close(). Returns a negative value if the catalog could not be opened.


On POSIX systems, this function call usually translates to a call to catopen(). In GNU libstdc++, it calls textdomain.

The actual catalog location is implementation-defined: for the catalog "sed" (message catalogs installed with the Unix utility 'sed') in German locale, for example, the file opened by this function call may be /usr/lib/nls/msg/de_DE/, /usr/lib/locale/de_DE/LC_MESSAGES/, or /usr/share/locale/de/LC_MESSAGES/


The following example demonstrated retrieval of messages: on a typical GNU/Linux system it reads from /usr/share/locale/de/LC_MESSAGES/

#include <iostream>
#include <locale>
int main()
    std::locale loc("de_DE.utf8");
    auto& facet = std::use_facet<std::messages<char>>(loc);
    auto cat ="sed", loc);
    if(cat < 0 )
        std::cout << "Could not open german \"sed\" message catalog\n";
        std::cout << "\"No match\" in German: "
                  << facet.get(cat, 0, 0, "No match") << '\n'
                  << "\"Memory exhausted\" in German: "
                  << facet.get(cat, 0, 0, "Memory exhausted") << '\n';

Possible output:

"No match" in German: Keine Übereinstimmung
"Memory exhausted" in German: Speicher erschöpft

See also