php中GB2312转UTF8的三种方法

<?
function encode_conver($subject,$function){
   switch ($function){
    case 1:
     $subject=iconv("GB2312","UTF-8",$subject);
     break;
    case 2:
     $subject=mb_convert_encoding($subject, "UTF-8", "GB2312");
     break;
    case 3:
     $subject=gb2utf8($subject);
     break;
   }
   return $subject;
}
function gb2utf8($string) 
{ 
 $ut=""; 
 $gb=file("./gbk.txt"); 
 $gb=explode("|",$gb[0]); 
 $utf=file("./utf8.txt"); 
 $utf=explode("|",$utf[0]); 
 $gb=array_flip($gb); 
 while ($string){ 
  $st=substr($string,0,1); 
  $string=substr($string,1); 
  if (ord($st)<128){ 
     $ut.=$st; 
  } else { 
   $st.=substr($string,0,1); 
   $string=substr($string,1);
   $ut.=$utf[$gb[$st]]; 
  } 
 } 
 return $ut; 
}?>