php gbk编码5c有关问题

<?php
$a = "哲";
$len = strlen("$a");
for($i=0;$i<$len;$i++){
printf("%0x",ord($a[$i]));
echo "\n";
}
printf("%0x",ord("\\"));
echo "\n";
echo chr(hexdec("d5")).chr(hexdec("5c"));
echo "\n";
?>

?如果单纯写echo "闸;则出现语法错误。PHP Parse error: syntax error, unexpected end of file in /home/keke/1.php on line 5

原因通过以上代码就可以明白了。