function check_bom($filename)
{
//bom头
$bomchars = "efbbbf";
//以二进制只读方式打开文件
$handle = fopen($filename, "rb");
//读取前3个字符
$contents = fread($handle, 3);
//将二进制转换为十六进制
$head = strval(bin2hex($contents));
//文件使用完毕，关闭之
fclose($handle);
//与bom头对比
return $head == $bomchars;
}