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 the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 8, 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
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 the
Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2,
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.
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 writers 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
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html