PHP 登录表单和注销按钮未正确显示 - PHP login form and logout button not showing properly

我刚开始学习PHP，在一个简单的登录页面工作时遇到了一些麻烦。当我第一次加载此脚本时，会打印文本"错误的密码/用户名"和注销按钮，但不打印登录表单。为什么会发生这种情况，我将如何更改代码以使登录表单和注销按钮按预期协同工作？

<?php
if (isset($_POST['log_out'])) { // If the page was reloaded as a result of the user having clicked the logout button,
session_destroy(); // kill session.
}
session_start(); // Start a new session with
$_SESSION['user'] = 'foo'; // a static username, and
$_SESSION['pass'] = 'bar'; // a static password.
// If I insert $_SESSION['logged_in'] = 'false'; here to start things off, a blank alert box will be returned no matter from where on the page I alert() the value with JS. On the other hand, without this line the same alert will return "1" both here and further down in the script.
if (($_POST['username'] == $_SESSION['user']) && ($_POST['password'] == $_SESSION['pass'])) { // If the username and password filled in before the page reload match the static ones,
    $_SESSION['logged_in'] = true; // the user is logged in.
} else { // If there is no match ...
    echo 'Wrong password/username.';
}
include("head.php"); // HTML snippet with everything from the DOCTYPE to the opening BODY tag.
?>
            <div> // HTML interlude ...
<?php
// If the user is logged in, print out a logout button in HTML at the top of the page:
if (isset($_SESSION['logged_in']) && ($_SESSION['logged_in'] == true)) {
    echo '          <form action="index.php" method="post">';
    echo '            <input type="submit" name="log_out" value="Log out">';
    echo '          </form>';
}
?>
                <p>HTML interlude ...</p>
<?php
// If the user is not logged in, print out a login form in HTML at the bottom of the page:
if ($_SESSION['logged_in'] != true) {
    echo '            <form action="index.php" method="post">';
    echo '              <label for="username">Username</label><br>';
    echo '              <input type="text" name="username" id="username"><br>';
    echo '              <label for="password">Password</label><br>';
    echo '              <input type="text" name="password" id="password"><br>';
    echo '              <input type="submit" name="submit" id="submit" value="Log in">';
    echo '            </form>';
}
?>
            </div>
<?php include("footer.php"); ?>

if (($_POST['username'] == $_SESSION['user']) && ($_POST['password'] == $_SESSION['pass'])) { the static ones,
    $_SESSION['logged_in'] = true; // the user is logged in.
} else { 
    echo 'Wrong password/username.';
}

当页面第一次加载时，这部分将显示"错误的密码/用户名"，因为如果没有来自$_POST['username']，条件将为假。

将条件isset($_POST['username']) && isset($_POST['password'])添加到这两个选项。这样：

if(isset($_POST['username']) && isset($_POST['password'])){
    if (($_POST['username'] == $_SESSION['user']) && ($_POST['password'] == $_SESSION['pass'])) { the static ones,
        $_SESSION['logged_in'] = true; // the user is logged in.
    } else { 
        echo 'Wrong password/username.';
    }
}

这样，在

首次加载页面时不会评估任何内容，而只会在发布凭据时进行评估。

通过调试脚本可以发现：将期望存储到变量中并打印出来，例如：

$isLoggedIn = $_SESSION['logged_in']; # Give things a name! (always useful)
echo 'isLoggedIn: ', var_dump($isLoggedIn), "'n"; # debugging
if ($isLoggedIn != true) {
    echo '            <form action="index.php" method="post">';
    echo '              <label for="username">Username</label><br>';
    echo '              <input type="text" name="username" id="username"><br>';
    echo '              <label for="password">Password</label><br>';
    echo '              <input type="text" name="password" id="password"><br>';
    echo '              <input type="submit" name="submit" id="submit" value="Log in">';
    echo '            </form>';
}

第一次加载页面时，除非您传递了所需的帖子变量，否则您的条件检查

if (($_POST['username'] == $_SESSION['user']) && ($_POST['password'] == $_SESSION['pass']))

将失败，因此显示Wrong password/username.消息。

代码看起来不错，实际上对于"只是学习"的人来说做得很好。

鉴于代码没有明显的问题（一些粗糙的边缘 - 在比较布尔值时，您应该考虑使用"==="而不是"=="），那么问题可能是会话。

尝试。。。

print_r（$_SESSION）;

紧跟在 session_start（）之后，紧接在选择是否显示注销按钮的条件之前。

每次您不将参数发布到页面以及发布错误的值时，都会显示错误的用户名消息。试试这个：

if (($_POST['username'])
    && ($_POST['username'] == $_SESSION['user']) 
    && ($_POST['password'] == $_SESSION['pass'])) {

顺便说一句，会话不是存储用户名和密码的好存储库 - 它特定于当前用户。对于多用户系统，这些将存储在单独的数据库中，例如

if (($_POST['username']) && lookup($_POST['username'], $_POST['password'])) {
...