使用未设置的全局变量时不显示回显

Question

我已经在配置页面、$_SESSION['logged_out'] = 1; 和索引页面上启动了一个会话：

if(isset($_SESSION['logged_out']))
{
     echo "You have been logged out !";
     unset($_SESSION['logged_out']);
}

但回声不工作，就像未设置在他面前。我不明白为什么，请帮助我。 编辑： 配置页面：

<?php
ini_set('display_errors',1); 
error_reporting(E_ALL);
ob_start();
session_start();
include 'connection.php';
include 'functions.php';

$logged_in = 0;
if(isset($_SESSION['username']) && isset($_SESSION['password']))
{
    $username = sec($link, $_SESSION['username']);
    $password = sec($link, $_SESSION['password']);
    $udata = get_row($link, "SELECT * FROM accounts WHERE Username= '$username' && Password= MD5('$password')");
    if(isset($udata['ID']))
    {
        $logged_in = 1;
        if(isset($_GET['logout']))
        {
            unset($_SESSION['username']);
            unset($_SESSION['password']);
            $_SESSION['logged_out'] = "1";
            mysqli_query($link, "UPDATE accounts SET rpgon = '0' WHERE Username = '$username'");
            header('location: index.php');
        }
    }
} ?>

索引页：

if(isset($_SESSION['logged_out']))
{
    echo "You have been logged out !";  
    unset($_SESSION['logged_out']);
}?>

就是这样……

Answer 1

如果echo 没有显示任何内容，是因为if 条件被评估为false。这意味着$_SESSION['logged_out'] 未设置。

Answer 2

您必须在使用$_SESSION 的每个页面上start_session()。事实上，如果您在网站的任何地方使用 $_SESSION，最好在您的所有页面上启动它。

所以在第一个<?php 之后添加start_session() 以确保它始终为所有页面启动

<php
start_session();

 . . .

if(isset($_SESSION['logged_out']))
{
     echo "You have been logged out !";
     unset($_SESSION['logged_out']);
}

在提供额外信息后添加

我认为这可能是你的问题之一

$udata = get_row($link, 
                 "SELECT * FROM accounts 
                  WHERE Username= '$username' 
                     && Password= MD5('$password')"
                 );

&& 应该是AND，那么这个查询应该返回一个结果。你真的应该像这样检查所有查询命令的结果状态：

<?php
ini_set('display_errors',1); 
error_reporting(E_ALL);
session_start();

ob_start();

include 'connection.php';
include 'functions.php';

$logged_in = 0;
if(isset($_SESSION['username']) && isset($_SESSION['password']))
{
    $username = sec($link, $_SESSION['username']);
    $password = sec($link, $_SESSION['password']);
    $udata = get_row($link, "SELECT * FROM accounts 
                             WHERE Username= '$username'
                               AND Password= MD5('$password')"
                     );

    // this would have shown the error in the sql query
    // if it had been here before
    if ( ! $udate ) {
        echo mysqli_error($link);
        exit;
    }


    // now this if will be executed
    // although this if is probably no longer required
    if(isset($udata['ID']))
    {
        $logged_in = 1;
        if(isset($_GET['logout']))
        {
            unset($_SESSION['username']);
            unset($_SESSION['password']);
            $_SESSION['logged_out'] = "1";
            mysqli_query($link, "UPDATE accounts SET rpgon = '0' WHERE Username = '$username'");
            header('location: index.php');

            // you should also follow a header() call with an exit;
            exit;
        }
    }
} 
?>