The textdomain function sets or retrieves the current message domain.
A message domain is a set of translatable msgid messages. Usually,
every software package has its own message domain. The domain name is used
to determine the message catalog where a translation is looked up; it must
be a non-empty string.
The current message domain is used by the gettext, ngettext
functions, and by the dgettext, dcgettext, dngettext and
dcngettext functions when called with a NULL domainname argument.
If domainname is not NULL, the current message domain is set to
domainname. The string the function stores internally is a copy of the
If domainname is NULL, the function returns the current message domain.
If successful, the textdomain function returns the current message
domain, after possibly changing it. The resulting string is valid until the
next textdomain call and must not be modified or freed. If a memory
allocation failure occurs, it sets errno to ENOMEM and returns
The following error can occur, among others:
Not enough memory available.
The return type ought to be const char *, but is char * to avoid
warnings in C code predating ANSI C.