Content-type: text/html Man page of catopen


Section: C Library Functions (3)
Index Return to Main Contents


catopen, NLSPATH - Opening a message catalog  


Standard C Library (, libc.a)  


#include <nl_types.h>

nl_catd catopen(
        const char *name,
        int oflag);  


Interfaces documented on this reference page conform to industry standards as follows:

catopen(): XPG4

Refer to the standards(5) reference page for more information about industry standards and associated tags.  


Specifies the message catalog to open. Specify the constant NL_CAT_LOCALE to open the message catalog for the locale set for the LC_MESSAGES variable; using NL_CAT_LOCALE conforms to the XPG4 standard. You can specify 0 (zero) for compatibility with XPG3; when oflag is set to zero, the locale set for the LANG variable determines the message catalog locale.  


The catopen() function opens a specified message catalog and returns a catalog descriptor that is used by the catgets() function to retrieve messages from the catalog.

The name parameter specifies the name of the message catalog to be opened. If name contains a / (slash), then name specifies a full pathname for the message catalog. Otherwise, the environment variable NLSPATH is used with substitutions based on the value of the name parameter and the value of the LC_MESSAGES setting. (See the i18n_intro(5) reference page for a description of LC_MESSAGES. See the NOTES section for a restriction that applies to use of the NLSPATH variable.)

NLSPATH is a colon-separated list of pathnames. The catopen() function makes variable substitutions in each pathname and attempts to open the specified catalog. If the open operation succeeds, the function returns the catalog descriptor for that catalog. If the open operation does not succeed, the function attempts to open the next pathname in the value of the NLSPATH environment variable.

If NLSPATH does not exist in the environment, then the function uses the following system default for NLSPATH:


Note that current industry standards do not specify the location of message catalogs, so application developers should consider this default to be platform specific.

If no message catalog can be opened in any of the components specified by NLSPATH, then catopen() returns a value of -1 cast to (nl_catd). This is not a valid catalog descriptor and causes subsequent calls to catgets() to return a pointer to the default message string.

The meaning of each variable in the NLSPATH environment variable is as follows: The value passed in the name parameter. The current locale name defined for the LC_MESSAGES category, for example, fr_BE.ISO8859-1. The language element of the current locale name, for example, fr. The territory element from the current locale name, for example, BE. The code set element from the current locale name, for example, ISO8859-1. A single % (percent sign) character.

For example, assume that the catopen() function specifies a catalog with the name, and the environment variables are set as follows:

NLSPATH=../%N:/usr/lib/nls/msg/%L/%N:/usr/lib/nls/msg/%l/%N LANG=fr_BE.ISO8859-1

Under these settings, the application searches for the catalog in the following order:

../ /usr/lib/nls/msg/fr_BE.ISO88591-1/ /usr/lib/nls/msg/fr/

The setlocale() function sets the value of the LC_MESSAGES category based on the values of the parameters to setlocale() and on the values of the LC_MESSAGES, LANG, and LC_ALL environment variables. The application program must call setlocale() to set the LC_MESSAGES category before calling catopen().

The descriptor for a message catalog remains valid in a process until one of the following occurs: The process closes the catalog descriptor. For example, the application executes a successful call to the catclose() function. The application executes a successful call to one of the exec() functions.

In addition, a change in the setting of LC_MESSAGES may invalidate descriptors for catalogs that are currently open.  


[Digital]  When running in a process whose effective user ID (set through the setuid() call) is root, the catopen() function ignores the NLSPATH setting and searches for message catalogs by using the default path /usr/lib/nls/msg/%L/%N. Therefore, if a program uses the setuid() call to change its effective user ID to root, either the program's message catalogs or links to its message catalogs must reside in default directories. This restriction exists to ensure system security. The restriction does not apply to a program whose real user ID is root. (In other words, the restriction does not apply to a program that is run by a user logged in to the root account.)

[Digital]  On Tru64 UNIX systems, a message catalog is not opened until the first catgets call that refers to the catalog. Therefore, the overhead associated with opening the catalog: Does not affect the speed of program startup Is eliminated altogether if the catalog is not used during a particular program execution cycle

[Digital]  Because the operation of opening the message catalog is deferred, the catopen() function always returns a valid catalog descriptor and sets errno for a very limited number of conditions. Therefore, applications cannot directly determine if the catalog open succeeds. They can indirectly check if the catalog open succeeds by comparing the address of the string that the catgets() function returns with the address of the default string. If the catgets() function returns the default string, then either the catalog open failed or the catalog does not contain the requested message.

[Digital]  Most languages are supported by multiple locales, each of which may use a different codeset. A user's locale setting may therefore be appropriate for the language in which messages are available but not in the correct character encoding. In such cases, it is useful to enable codeset conversion of message catalogs, so that users can receive messages in their native language when these are available, regardless of the encoding format supported by the catalog.

[Digital]  Codeset conversion of message catalogs is enabled by the presence of the .msg_conv-lc_message file in the /usr/share directory. The lc_message part of this file name must correspond to the value of the LC_MESSAGES part of the user's locale setting. The one-line content of this file has the following format:

alternate_lc_message from-codeset to-codeset

In this entry format: Is the locale for which message catalogs are available. Is the codeset of the message catalogs for that locale. Is the codeset to which messages need to be converted (the codeset of the user's locale).

[Digital]  The alternate_lc_message value replaces the user's locale in the %L position of the NLSPATH setting. The from-codeset and to-codeset values are used to find the appropriate codeset converter. These values must match the corresponding name segments for an available codeset converter or aliases for those name segments as specified in the /usr/lib/nls/loc/iconv.alias file. See iconv_intro(5) for more information about how codeset conversion works.

[Digital]  The operating system supplies .msg_conv-* files for the .UTF-8 locales, many of which have translated message catalogs available for *.ISO8859-1 or other encoding formats.

[Digital]  Note that the catgets() function first looks for a message catalog that matches the user's locale. Only if a catalog is not found does the function check for a .msg_conv-* file appropriate for the user's locale.

[Digital]  When codeset conversion of messages does occur, the converted messages remain in memory in a data structure associated with the opened catalog's descriptor for re-use by subsequent calls to the catgets() function. The catclose() function frees the memory allocated to converted messages for the descriptor of the catalog being closed.  


When successful, the catopen() function returns a catalog descriptor that can be used in calls to the catgets() and catclose() functions. When the catopen() function does not succeed, it returns a value of -1 cast to (nl_catd).  


If any of the following conditions occur, the catopen() function sets errno to the corresponding value.

[Digital]  See the NOTES section for information on the impact of deferred open. A signal was caught during the function. The length of the path of the file exceeds PATH_MAX, or a pathname component is longer than NAME_MAX. The name argument is NULL or points to an empty string. Insufficient memory is available.  


Functions: catgets(3), catclose(3), setlocale(3)

Commands: dspcat(1), dspmsg(1), extract(1), gencat(1), mkcatdefs(1), strextract(1), strmerge(1), trans(1)

Others: i18n_intro(5), iconv_intro(5), l10n_intro(5), standards(5)

Writing Software for the International Market delim off




This document was created by man2html, using the manual pages.
Time: 02:41:44 GMT, October 02, 2010