/*******************************
//GB转UTF-8编码
*******************************/
function gb2utf8($gbstr) {
 global $CODETABLE;
 if(trim($gbstr)=="") return $gbstr;
 if(empty($CODETABLE)){
  $filename = dirname(__FILE__)."/gb2312-utf8.table";
  $fp = fopen($filename,"r");
  while ($l = fgets($fp,15))
  { $CODETABLE[hexdec(substr($l, 0, 6))] = substr($l, 7, 6); }
  fclose($fp);
 }
 $ret = "";
 $utf8 = "";
 while ($gbstr) {
  if (ord(substr($gbstr, 0, 1)) > 127) {
   $thisW = substr($gbstr, 0, 2);
   $gbstr = substr($gbstr, 2, strlen($gbstr));
   $utf8 = "";
   @$utf8 = u2utf8(hexdec($CODETABLE[hexdec(bin2hex($thisW)) - 0x8080]));
   if($utf8!=""){
    for ($i = 0;$i < strlen($utf8);$i += 3)
     $ret .= chr(substr($utf8, $i, 3));
   }
  }
  else
  {
   $ret .= substr($gbstr, 0, 1);
   $gbstr = substr($gbstr, 1, strlen($gbstr));
  }
 }
 return $ret;
}
//Unicode转utf8
function u2utf8($c) {
 for ($i = 0;$i < count($c);$i++)
  $str = "";
 if ($c < 0x80) {
  $str .= $c;
 } else if ($c < 0x800) {
  $str .= (0xC0 | $c >> 6);
  $str .= (0x80 | $c & 0x3F);
 } else if ($c < 0x10000) {
  $str .= (0xE0 | $c >> 12);
  $str .= (0x80 | $c >> 6 & 0x3F);
  $str .= (0x80 | $c & 0x3F);
 } else if ($c < 0x200000) {
  $str .= (0xF0 | $c >> 18);
  $str .= (0x80 | $c >> 12 & 0x3F);
  $str .= (0x80 | $c >> 6 & 0x3F);
  $str .= (0x80 | $c & 0x3F);
 }
 return $str;
}

------解决方案--------------------
楼主看下这个帖子：http://neture.homeip.net/digiland/viewtopic.php?pid=39
下載地址osc_iconv.zip
里面有对照表的

如果需要非要使用，建议在php中打开iconv吧。

------解决方案--------------------
建议还是不要自己写了

------解决方案--------------------
强烈建议使用内置的,自己写对照表肯定不全
iconv 能处理的字符集有很多,自己写的肯定不能全包括