在会话中存储时间戳

<?php    
$user = $_POST['user_name'];
$pass = $_POST['user_pass'];

require ('db_connection.php');

// Hey, always escape input if necessary!
$result = mysql_query(sprintf("SELECT * FROM accounts WHERE user_Name='%s' AND user_Pass='%s'", mysql_real_escape_string($user), mysql_real_escape_string($pass));

if( mysql_num_rows( $result ) > 0)
{
    $array = mysql_fetch_assoc($result);    

    session_start();
    $_SESSION['user_id'] = $user;
    $_SESSION['login_time'] = time();
    header("Location:loggedin.php");            
}
else
{
    header("Location:login.php");
}
?>

现在，检查时间戳是否在允许的时间窗口内(1800秒是30分钟)

<?php
session_start();
if( !isset( $_SESSION['user_id'] ) || time() - $_SESSION['login_time'] > 1800)
{
    header("Location:login.php");
}
else
{
    // uncomment the next line to refresh the session, so it will expire after thirteen minutes of inactivity, and not thirteen minutes after login
    //$_SESSION['login_time'] = time();
    echo ( "this session is ". $_SESSION['user_id'] );
    //show rest of the page and all other content
}
?>

PHP是如何处理会话的，初学者很难理解。这可能会帮助他们概述会话的工作原理: 会话如何工作(自定义会话处理程序)

在会话中存储时间戳

<?php    
$user = $_POST['user_name'];
$pass = $_POST['user_pass'];

require ('db_connection.php');

// Hey, always escape input if necessary!
$result = mysql_query(sprintf("SELECT * FROM accounts WHERE user_Name='%s' AND user_Pass='%s'", mysql_real_escape_string($user), mysql_real_escape_string($pass));

if( mysql_num_rows( $result ) > 0)
{
    $array = mysql_fetch_assoc($result);    

    session_start();
    $_SESSION['user_id'] = $user;
    $_SESSION['login_time'] = time();
    header("Location:loggedin.php");            
}
else
{
    header("Location:login.php");
}
?>

现在，检查时间戳是否在允许的时间窗口内(1800秒是30分钟)

<?php
session_start();
if( !isset( $_SESSION['user_id'] ) || time() - $_SESSION['login_time'] > 1800)
{
    header("Location:login.php");
}
else
{
    // uncomment the next line to refresh the session, so it will expire after thirteen minutes of inactivity, and not thirteen minutes after login
    //$_SESSION['login_time'] = time();
    echo ( "this session is ". $_SESSION['user_id'] );
    //show rest of the page and all other content
}
?>

使用下面这样的函数其实很简单。它使用数据库表名'sessions'与字段'id'和'time'。

每次当用户再次访问您的站点或服务时，您都应该调用这个函数来检查它的返回值是否为TRUE。如果是FALSE，用户已经过期，会话将被销毁(注意:这个函数使用一个数据库类来连接和查询数据库，当然你也可以在你的函数中这样做或类似的事情):

function session_timeout_ok() {
    global $db;
    $timeout = SESSION_TIMEOUT; //const, e.g. 6 * 60 for 6 minutes
    $ok = false;
    $session_id = session_id();
    $sql = "SELECT time FROM sessions WHERE session_id = '".$session_id."'";
    $rows = $db->query($sql);
    if ($rows === false) {
        //Timestamp could not be read
        $ok = FALSE;
    }
    else {
        //Timestamp was read succesfully
        if (count($rows) > 0) {
            $zeile = $rows[0];
            $time_past = $zeile['time'];
            if ( $timeout + $time_past < time() ) {
                //Time has expired
                session_destroy();
                $sql = "DELETE FROM sessions WHERE session_id = '" . $session_id . "'";
                $affected = $db -> query($sql);
                $ok = FALSE;
            }
            else {
                //Time is okay
                $ok = TRUE;
                $sql = "UPDATE sessions SET time='" . time() . "' WHERE session_id = '" . $session_id . "'";
                $erg = $db -> query($sql);
                if ($erg == false) {
                    //DB error
                }
            }
        }
        else {
            //Session is new, write it to database table sessions
            $sql = "INSERT INTO sessions(session_id,time) VALUES ('".$session_id."','".time()."')";
            $res = $db->query($sql);
            if ($res === FALSE) {
                //Database error
                $ok = false;
            }
            $ok = true;
        }
        return $ok;
    }
    return $ok;
}

使用session_set_cookie_params函数来做到这一点。

有必要在session_start()调用之前调用这个函数。

试试这个:

$lifetime = strtotime('+30 minutes', 0);

session_set_cookie_params($lifetime);

session_start();

详见:http://php.net/manual/function.session-set-cookie-params.php

if (isSet($_SESSION['started'])){
    if((mktime() - $_SESSION['started'] - 60*30) > 0){
        //Logout, destroy session, etc.
    }
}
else {
    $_SESSION['started'] = mktime();
}