PHP：日本語文字列を指定文字数で分割して配列に

mb_language('Japanese');
mb_internal_encoding('SJIS');

$str = "あいうえおかきくけこaiueo";
$array = mb_str_split($str, 4);
print_r($array);

function mb_str_split($str, $length = 1) {

if ($length <1) return FALSE;

$result = array();

for ($i = 0; $i <mb_strlen($str); $i += $length) {

$result[] = mb_substr($str, $i, $length);

}

return $result;

}
http://www.developer0000.jp/2007/11/28/1975/