<?php
$foo = "???";

if(preg_match("/\w+/", $foo, $bar)) {
  echo "preg_match default locale => Match\n";
} else {
  echo "preg_match default locale => No Match\n";
}
if(ereg("[[:alnum:]]+", $foo, $bar)) {
  echo "ereg       default locale => Match\n";
} else {
  echo "ereg       default locale => No Match\n";
}
 
setlocale("LC_CTYPE", "no_NO");

if(preg_match("/\w+/", $foo, $bar)) {
  echo "preg_match  no_No  locale => Match\n";
} else {
  echo "preg_match  no_No  locale => No Match\n";
}
if(ereg("[[:alnum:]]+", $foo, $bar)) {
  echo "ereg        no_No  locale => Match\n";
} else {
  echo "ereg        no_No  locale => No Match\n";
}
?>

produses following output:
preg_match default locale => No Match
ereg       default locale => No Match
preg_match  no_No  locale => Match
ereg        no_No  locale => No Match