一个更简洁的php字符串截取

<?php   
// Cut a string   
function str_cut($string, $start, $width="", $trimmarker="", $encoding="UTF-8")   
{   
     if ($width == "") {   
         $width = mb_strwidth($string,"UTF-8");   
     }   
     return mb_strimwidth($string, $start, $width, $trimmarker, $encoding);   
}
$first_str   = str_cut("eb163.com是web编程站的域名，pr值4",4,6);
$sencond_str = str_cut("eb163.comeb163.comeb163.comeb163.com",4,6);
$third_str   = str_cut("编程站学编程学编程就上编程站",4,6);

echo($first_str."<br />");
echo($sencond_str."<br />");
echo($third_str."<br />");
?>