# std::messages::open, std::messages::do_open

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< cpp‎ | locale‎ | messages

Defined in header `<locale>` |  |
public: catalog open( const std::basic_string<char>& name, const std::locale& loc ) const; | (1) |
protected: virtual catalog do_open( const std::basic_string<char>& name, const std::locale& loc ) const; | (2) |

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().

### Parameters

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.

### Notes

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/sed.cat`, `/usr/lib/locale/de_DE/LC_MESSAGES/sed.cat`, or `/usr/share/locale/de/LC_MESSAGES/sed.mo`.

### Example

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

Run this code

    #include <iostream>
    #include <locale>

    int main()
    {
        std::locale loc("de_DE.utf8");
        std::cout.imbue(loc);
        auto& facet = std::use_facet<std::messages<char>>(loc);
        auto cat = facet.open("sed", loc);
        if(cat < 0 )
            std::cout << "Could not open german \"sed\" message catalog\n";
        else
            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';
        facet.close(cat);
    }

Output:

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

### See also

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