Questions about intercepting GBK strings ~

Intercept the GBK string problem ~ ~ ~
This is a function that intercepts the GBK string:

PHP Code

  
   function  gb_substr ($str,  $len) {              $count  = 0;              for ($i =0;  $i < strlen ($STR);  $i + +) {                  if ($count  = =  $len) break  ;                  if (Preg_match ("/[\x80-\xff]/",  substr ($str,  $i, 1))) {        + + + $i;          }                  + + $count;                      }              Return   substr ($str, 0,  $i);        }

My question is, GBK and GB2312 each character is not sure to be 2 bytes? The length of the direct use of the intercept will not be finished?
For example, I want to intercept 3 characters: 3*2=6 is the position I want to intercept to 6.

You think so, right?

------Solution--------------------
Using the MB series function, the GBK is two characters non-ASCII, ASCII or 1 bytes.
------Solution--------------------
No, because there are numbers or characters that may contain ASCII code

discuss
This is a function that intercepts the GBK string:
PHP Code

function Gb_substr ($STR, $len) {
$count = 0;
for ($i =0; $i < strlen ($STR); $i + +) {
if ($count = = $len) break ...

