---
name: "catopen"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/catopen"
---

# catopen(3)

open message catalog

## NAME

**catopen** – open message catalog

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<nl\_types.h\>**

*nl\_catd*\

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

## DESCRIPTION

The **catopen**() function opens the message catalog specified by *name* and returns a message catalog descriptor. If *name* contains a ‘/’ then *name* specifies the full pathname for the message catalog, otherwise the value of the environment variable NLSPATH is used with the following substitutions:

- %N

  The value of the *name* argument.

- %L

  The value of the LANG environment variable or the LC\_MESSAGES category (see below).

- %l

  The language element from the LANG environment variable or from the LC\_MESSAGES category.

- %t

  The territory element from the LANG environment variable or from the LC\_MESSAGES category.

- %c

  The codeset element from the LANG environment variable or from the LC\_MESSAGES category.

- %%

  A single % character.

An empty string is substituted for undefined values.

Path names templates defined in NLSPATH are separated by colons ( ‘:’). A leading or two adjacent colons is equivalent to specifying %N.

If the *oflag* argument is set to the NL\_CAT\_LOCALE constant, LC\_MESSAGES locale category used to open the message catalog; using NL\_CAT\_LOCALE conforms to the X/Open Portability Guide Issue 4 (“XPG4”) standard. You can specify 0 for compatibility with X/Open Portability Guide Issue 3 (“XPG3”); when *oflag* is set to 0, the LANG environment variable determines the message catalog locale.

A message catalog descriptor remains valid in a process until that process closes it, or until a successful call to one of the [exec(3)](/exec/3.md) function.

## RETURN VALUES

Upon successful completion, **catopen**() returns a message catalog descriptor. Otherwise, (nl\_catd) -1 is returned and *errno* is set to indicate the error.

## ERRORS

- \[EINVAL\]

  Argument *name* does not point to a valid message catalog, or catalog is corrupt.

- \[ENAMETOOLONG\]

  An entire path to the message catalog exceeded 1024 characters.

- \[ENOENT\]

  The named message catalog does not exists, or the *name* argument points to an empty string.

- \[ENOMEM\]

  Insufficient memory is available.

## SEE ALSO

[gencat(1)](/gencat/1.md), [catclose(3)](/catclose/3.md), [catgets(3)](/catgets/3.md), [setlocale(3)](/setlocale/3.md)

## STANDARDS

The **catopen**() function conforms to IEEE Std 1003.1-2001 (“POSIX.1”).