php中英字符串截取

<?php 

@header('Content-type: text/html; charset=UTF-8');
function Ctruncate($str = '', $len = 0, $etc = '...')
{
if(0 == $len) return "";

$str_len = preg_match_all('/[\x00-\x7F\xC0-\xFD]/', $str, $dummy);
if($len >= $str_len)
{
return $str;
}
else
{
$newstr = mb_substr($str,0,$len,'utf-8');
return $newstr.$etc;
}
} 

$a = "a的flhjqowihvjnjxlkcoiqyeruqwheridsiomosdifgoiioqwerhiwerqwer";

echo Ctruncate($a, "10");

?>