Manual Reference Pages  - CATOPEN (3)


catopen, catclose - open/close a message catalog


     Linux Notes


#include <nl_types.h>

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

int catclose(nl_catd catalog);


The function catopen() opens a message catalog and returns a catalog descriptor. The descriptor remains valid until catclose() or execve(2). If a file descriptor is used to implement catalog descriptors then the FD_CLOEXEC flag will be set.

The argument name specifies the name of the message catalog to be opened. If name specifies and absolute path (i.e., contains a / ), then name specifies a pathname for the message catalog. Otherwise, the environment variable NLSPATH is used with name substituted for %N (see locale(7)). It is unspecified whether NLSPATH will be used when the process has root privileges. If NLSPATH does not exist in the environment, or if a message catalog cannot be opened in any of the paths specified by it, then an implementation defined path is used. This latter default path may depend on the LC_MESSAGES locale setting when the flag argument is NL_CAT_LOCALE and on the LANG environment variable when the flag argument is 0. Changing the LC_MESSAGES part of the locale may invalidate open catalog descriptors.

The flag argument to catopen() is used to indicate the source for the language to use. If it is set to NL_CAT_LOCALE then it will use the current locale setting for LC_MESSAGES. Otherwise it will use the LANG environment variable.

The function catclose() closes the message catalog identified by catalog. It invalidates any subsequent references to the message catalog defined by catalog.


The function catopen() returns a message catalog descriptor of type nl_catd on success. On failure, it returns (nl_catd) -1 and sets errno to indicate the error. The possible error values include all possible values for the open(2) call.

The function catclose() returns 0 on success, or -1 on failure.


  May be the source of the LC_MESSAGES locale setting, and thus determine the language to use if flag is set to NL_CAT_LOCALE.
LANG The language to use if flag is 0.


POSIX.1-2001. It is unclear what the source was for the constants MCLoadBySet and MCLoadAll (see below).


The above is the POSIX.1-2001 description. The glibc value for NL_CAT_LOCALE is 1. (Compare MCLoadAll below.) The default path varies, but usually looks at a number of places below /usr/share/locale.

    Linux Notes

These functions are available for Linux since libc 4.4.4c. In the case of linux libc4 and libc5, the catalog descriptor nl_catd is a mmap(2)’ed area of memory and not a file descriptor. The flag argument to catopen() should be either MCLoadBySet (=0) or MCLoadAll (=1). The former value indicates that a set from the catalog is to be loaded when needed, whereas the latter causes the initial call to catopen() to load the entire catalog into memory. The default search path varies, but usually looks at a number of places below /etc/locale and /usr/lib/locale.


catgets(3), setlocale(3)


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GNU CATOPEN (3) 2001-12-14
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