PHP encoding conversion realizes gbk encoding conversion to utf8

class gb2utf8
{
var $gb; // The gb2312 string to be converted
var $utf8; // The converted utf8 string
var $codetable; // Array of gb2312 code files used during the conversion process
var $errormsg; // Error message during the conversion process
function gb2utf8($instr="")
{
$this- >gb=$instr;
$this->setgb2312();
($this->gb=="")?0:$this->convert();
}
 function setgb2312($instr="gb2312.txt")
{ // Set gb2312 code file, the default is gb2312.txt
$this->errormsg="";
$tmp=@file($instr );
 if (!$tmp) {
 $this->errormsg="no gb2312";
 return false;
 }
$this->codetable=array();
while(list($key,$ value)=each($tmp)) {
$this->codetable[hexdec(substr($value,0,6))]=substr($value,7,6);
}
} //(script Xuetangbbs.it-home.org)
function convert()
{ // Convert gb2312 string to utf8 string, $gb needs to be set in advance
$this->utf8=" ";
if(!trim($this->gb) || $this->errormsg!="") {
return ($this->utf8=$this->errormsg);
}
 $str=$this->gb;
while($str) {
if (ord(substr($str,0,1))>127)
{
$tmp =substr($str,0,2);
$str=substr($str,2,strlen($str));
$tmp=$this->u2utf8(hexdec($this->codetable[hexdec (bin2hex($tmp))-0x8080]));
for($i=0;$i$this->utf8.=chr(substr($tmp ,$i,3));
}
else
{
$tmp=substr($str,0,1);
$str=substr($str,1,strlen($str));
$this- >utf8.=$tmp;
}
}
return $this->utf8;
}
function u2utf8($instr)
{
for($i=0;$ i$str="";
if ($instr < 0x80) {
$str.=ord($instr);
}
else if ($instr < 0x800 ) {
$str.=(0xc0 | $instr>>6);
$str.=(0x80 | $instr & 0x3f);
}
else if ($instr < 0x10000) {
$str.= (0xe0 | $instr>>12);
$str.=(0x80 | $instr>>6 & 0x3f);
$str.=(0x80 | $instr & 0x3f);
}
else if ($ instr < 0x200000) {
$str.=(0xf0 | $instr>>18);
$str.=(0x80 | $instr>>12 & 0x3f);
$str.=(0x80 | $instr> ;>6 & 0x3f);
$str.=(0x80 | $instr & 0x3f);
}
return $str;
}
}
?>

Test example:

//php encoding conversion
header("content-type: image/png");
$im = imagecreate(400,300);
$black = imagecolorallocate($im, 0, 0,0);
$white = imagecolorallocate($im, 184,44,6);
include("gb2utf8.php");
$obj=new gb2utf8();
$obj->gb="123abc China 456def test is correct";
$obj->convert();
imagettftext($im, 20, 0, 5, 50, $white, "simkai.ttf", $obj->utf8);
imagepng( $im);
imagedestroy($im);
?>

Code description: The font file needs to be set correctly. Please first confirm that you can use font to output English directly (without using gb2utf8).