PHP code for GB2312 and UTF8 encoding conversion

Class GB2UTF8
{
var $gb; // GB2312 string to be converted
var $utf8; // 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 the 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);
}
}
function Convert()
{ // To convert GB2312 string to UTF8 string, you need to set $gb
$this->utf8="";
if(!trim($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 it and see the effect:

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="123abcChina 456def test is correct";
$obj->Convert();
ImageTTFText($im, 20, 0, 5, 50, $white, "SIMKAI.TTF", $obj->utf8);
ImagePNG($im);
ImageDestroy ($im);
?>

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