PHP分割中文字符串为数组

function mb_str_split($str,$split_length=1,$charset="UTF-8"){
  if(func_num_args()==1){
    return preg_split('/(?<!^)(?!$)/u', $str);
  }
  if($split_length<1)return false;
  $len = mb_strlen($str, $charset);
  $arr = array();
  for($i=0;$i<$len;$i+=$split_length){
    $s = mb_substr($str, $i, $split_length, $charset);
    $arr[] = $s;
  }
  return $arr;
}
print_r(mb_str_split('lizhenqiu.com'));
print_r(mb_str_split('中文字符串'));