//在线人数

function online_users() {
$filename='online.txt'; //数据文件
$cookiename='Nanlon_OnLineCount'; //Cookie名称
$onlinetime=30; //在线有效时间
$online=file($filename); 
$nowtime=$_SERVER['REQUEST_TIME']; 
$nowonline=array(); 
foreach($online as $line){ 
    $row=explode('|',$line); 
    $sesstime=trim($row[1]); 
    if(($nowtime - $sesstime)<=$onlinetime){
        $nowonline[$row[0]]=$sesstime;
    } 
} 
if(isset($_COOKIE[$cookiename])){
    $uid=$_COOKIE[$cookiename]; 
}else{
    $vid=0;
    do{
        $vid++; 
        $uid='U'.$vid; 
    }while(array_key_exists($uid,$nowonline)); 
    setcookie($cookiename,$uid); 
} 
$nowonline[$uid]=$nowtime;
$total_online=count($nowonline); 
if($fp=@fopen($filename,'w')){ 
    if(flock($fp,LOCK_EX)){ 
        rewind($fp); 
        foreach($nowonline as $fuid=>$ftime){ 
            $fline=$fuid.'|'.$ftime."\n"; 
            @fputs($fp,$fline); 
        } 
        flock($fp,LOCK_UN); 
        fclose($fp); 
    } 
} 
echo "$total_online"; 

}

footer.php在适当位置添加下列代码

<center>

当前在线<?php echo online_users() ?>人