The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group


catopen - open a message catalog


#include <nl_types.h>

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


The catopen() function shall open a message catalog and return a message catalog descriptor. The name argument specifies the name of the message catalog to be opened. If name contains a '/', then name specifies a complete name for the message catalog. Otherwise, the environment variable NLSPATH is used with name substituted for the %N conversion specification (see XBD Environment Variables). If NLSPATH exists in the environment when the process starts, then if the process has appropriate privileges, the behavior of catopen() is undefined. If NLSPATH does not exist in the environment, or if a message catalog cannot be found in any of the components specified by NLSPATH, then an implementation-defined default path shall be used. This default may be affected by the setting of LC_MESSAGES if the value of oflag is NL_CAT_LOCALE, or the LANG environment variable if oflag is 0.

A message catalog descriptor shall remain 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 catalogs.

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

If the value of the oflag argument is 0, the LANG environment variable is used to locate the catalog 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 catalog (see XBD Internationalization Variables ).


Upon successful completion, catopen() shall return a message catalog descriptor for use on subsequent calls to catgets() and catclose(). Otherwise, catopen() shall return (nl_catd) -1 and set errno to indicate the error.


The catopen() function may fail if:

Search permission is denied for the component of the path prefix of the message catalog or read permission is denied for the message catalog.
All file descriptors available to the process are currently open.
The length of a component of a pathname is longer than {NAME_MAX}.
The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an intermediate result with a length that exceeds {PATH_MAX}.
Too many files are currently open in the system.
The message catalog does not exist or the name argument points to an empty string.
Insufficient storage space is available.
A component of the path prefix of the message catalog names an existing file that is neither a directory nor a symbolic link to a directory, or the pathname of the message catalog contains at least one non- <slash> character and ends with one or more trailing <slash> characters and the last pathname component names an existing file that is neither a directory nor a symbolic link to a directory.

The following sections are informative.




Some implementations of catopen() use malloc() to allocate space for internal buffer areas. The catopen() function may fail if there is insufficient storage space available to accommodate these buffers.

Conforming applications must assume that message catalog descriptors are not valid after a call to one of the exec functions.

Application developers should be aware that guidelines for the location of message catalogs have not yet been developed. Therefore they should take care to avoid conflicting with catalogs used by other applications and the standard utilities.






catclose, catgets

XBD Environment Variables, <fcntl.h>, <nl_types.h>,


First released in Issue 2.

Issue 7

Austin Group Interpretation 1003.1-2001 #143 is applied.

SD5-XBD-ERN-4 is applied, changing the definition of the [EMFILE] error.

The catopen() function is moved from the XSI option to the Base.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0045 [324] is applied.

End of informative text.


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