The catopen() function opens a message catalog and returns a message catalog descriptor. name specifies the name of the message catalog to be opened. If name contains a "/", then name specifies a complete pathname for the message catalog; otherwise, the environment variable NLSPATH is used and /usr/lib/locale/locale/LC_MESSAGES must exist. If NLSPATH does not exist in the environment, or if a message catalog cannot be opened in any of the paths specified by NLSPATH, then the default path /usr/lib/locale/locale/LC_MESSAGES is used. In the "C" locale, catopen() will always succeed without checking the default search path.

The names of message catalogs and their location in the filesystem can vary from one system to another. Individual applications can choose to name or locate message catalogs according to their own special needs. A mechanism is therefore required to specify where the catalog resides.

The NLSPATH variable provides both the location of message catalogs, in the form of a search path, and the naming conventions associated with message catalog files. For example:

NLSPATH=/nlslib/%L/%N.cat:/nlslib/%N/%L 

The metacharacter % introduces a substitution field, where %L substitutes the current setting of either the LANG environment variable, if the value of oflag is 0, or the LC_MESSAGES category, if the value of oflag is NL_CAT_LOCALE, and %N substitutes the value of the name parameter passed to catopen(). Thus, in the above example, catopen() will search in /nlslib/$LANG/name.cat, if oflag is 0, or in /nlslib/{LC_MESSAGES}/name.cat, if oflag is NL_CAT_LOCALE.

The NLSPATH variable will normally be set up on a system wide basis (in /etc/profile) and thus makes the location and naming conventions associated with message catalogs transparent to both programs and users.

The full set of metacharacters is:

%N

The value of the name parameter passed to catopen().

%L

The value of LANG or LC_MESSAGES.

%l

The value of the language element of LANG or LC_MESSAGES.

%t

The value of the territory element of LANG or LC_MESSAGES.

%c

The value of the codeset element of LANG or LC_MESSAGES.

%%

A single %.

The LANG environment variable provides the ability to specify the user's requirements for native languages, local customs and character set, as an ASCII string in the form

LANG=language[_territory[.codeset]]

A user who speaks German as it is spoken in Austria and has a terminal which operates in ISO 8859/1 codeset, would want the setting of the LANG variable to be

LANG=De_A.88591

With this setting it should be possible for that user to find any relevant catalogs should they exist.

Should the LANG variable not be set, the value of LC_MESSAGES as returned by setlocale() is used. If this is NULL, the default path as defined in <nl_types.h> is used.

A message catalogue descriptor remains valid in a process until that process closes it, or a successful call to one of the exec functions. A change in the setting of the LC_MESSAGES category may invalidate existing open catalogues.

If a file descriptor is used to implement message catalogue descriptors, the FD_CLOEXEC flag will be set; see <fcntl.h>.

If the value of oflag argument is 0, the LANG environment variable is used to locate the catalogue without regard to the LC_MESSAGES category. If the oflag argument is NL_CAT_LOCALE, the LC_MESSAGES category is used to locate the message catalogue.

The catclose() function closes the message catalog identified by catd. If a file descriptor is used to implement the type nl_catd, that file descriptor will be closed.

Upon successful completion, catopen() returns a message catalog descriptor for use on subsequent calls to catgets() and catclose(). Otherwise it returns (nl_catd) -1.

Upon successful completion, catclose() returns 0. Otherwise it returns -1 and sets errno to indicate the error.

The catopen() function may fail if:

EACCES

Search permission is denied for the component of the path prefix of the message catalogue or read permission is denied for the message catalogue.

EMFILE

There are OPEN_MAX file descriptors currently open in the calling process.

ENAMETOOLONG

The length of the pathname of the message catalogue exceeds PATH_MAX, or a pathname component is longer than NAME_MAX.

ENAMETOOLONG

Pathname resolution of a symbolic link produced an intermediate result whose length exceeds PATH_MAX.

ENFILE

Too many files are currently open in the system.

ENOENT

The message catalogue does not exist or the name argument points to an empty string.

ENOMEM

Insufficient storage space is available.

ENOTDIR

A component of the path prefix of the message catalogue is not a directory.

The catclose() function may fail if:

EBADF

The catalogue descriptor is not valid.

EINTR

The catclose() function was interrupted by a signal.

The catopen() and catclose() functions can be used safely in multithreaded applications, as long as setlocale(3C) is not being called to change the locale.

See attributes(5) for descriptions of the following attributes:

gencat(1), catgets(3C), gettext(3C), nl_types(3HEAD), setlocale(3C), attributes(5), environ(5)