login && session

运用session保存用户的登录状态。

session相关：

session_start();               //激活变量$_SESSION[]
$_SESSION['username'] = $username;          
unset($_SESSION['username']);        //清空变量
session_destroy();           //清除会话

本例实现的功能：

login,   logout

后台：process.php

    // login
    if(@$_POST["login_submit"]){
        $str = "SELECT * FROM users WHERE username='$_POST[username]' and password='$_POST[password]'";
        $res = mysql_query($str);
        if(mysql_fetch_array($res)){
            session_start();
            $_SESSION['username'] = $_POST['username'];
            exit($_SESSION['username'].'欢迎你！点击此处 <a href="index.php">返回首页</a><br />');
        }else
            exit('登录失败！点击此处 <a href="javascript:history.back(-1);">返回</a>');
    }

    // logout
    if(@$_GET["action"] == "logout"){
        session_start();
        unset($_SESSION['username']);
        session_destroy();
        exit('注销成功！点击此处 <a href="index.php">返回首页</a><br />');
    }

前台: login.php

            <?php
                session_start();                //!!!!!!
                if(empty($_SESSION["username"])){
                    echo             
                    "<div><a href='register.php'>register</a></div>
                    <form action='process.php' method='post'>
                        username:<input type='text' name='username' /><br/>
                        password:<input type='password' name='password' /><br/>
                        <input type='submit' name='login_submit' value='login'/>
                    </form>";
                }else{
                    echo 
                    "<div>
                        <div><a href='home.php?'>{$_SESSION["username"]}</a></div>
                        <div><a href='process.php?action=logout'>注销</a></div>
                    </div>";
                }
            ?>