$a='大客户疯狂的顺口溜';
function substr_utf8($string,$start,$length){
return join("",array_slice(preg_split("//u",$string,-1,PREG_SPLIT_NO_EMPTY),$start,$length));
}
echo substr_utf8($a,2,4); //户疯狂的
2
$b='科技股和扩大发挥港口';
echo mb_strlen($b,'utf8');//10
echo mb_substr($b,3,1,'utf8'); //和