我在$_SESSION变量方面遇到了很多麻烦。我正在尝试为用户创建一种登录和注销方式。我可以登录用户，但切换页面时似乎无法维持会话。当用户正确登录时，他们将被带到profile.php. 但是，如果我返回index.php打印以下错误：
Notice: Undefined index: login in /Applications/MAMP/htdocs/www/Shared sites/userlogreg/index.php on line 3
我对此很陌生，但从 SO 和其他地方看，我似乎无法弄清楚。任何帮助，将不胜感激。
索引.php
<?php
session_start();
if ($_SESSION['login'] == 1) {
echo "<h1>Logged in!</h1>";
} else {
echo "<h1>Not logged in</h1><br/>";
}
?>
<!DOCTYPE HTML>
<html>
<head>
<title>Index page</title>
</head>
<body>
<h2>Login</h2>
<form action="login.php" method="POST">
<div>
<label for="emailSignIn">Email:</label>
<input type="email" name="email" placeholder="Email" required="required" />
</div>
<div>
<label for="passwordSignIn">Password:</label>
<input type="password" name="password" placeholder="Password" required="required" />
</div>
<input type="submit" name="submit" value="Sign in" />
</form>
<h2>Register</h2>
<form action="register.php" method="POST">
<div>
<label for="firstnameRegister">First name:</label>
<input type="text" name="firstname" placeholder="First name" required="required" />
</div>
<div>
<label for="lastnameRegister">Last name:</label>
<input type="text" name="lastname" placeholder="Last name" required="required" />
</div>
<div>
<label for="emailRegister">Email:</label>
<input type="email" name="email" placeholder="Email" required="required" />
</div>
<div>
<label for="passwordRegister">Password:</label>
<input type="password" name="password" placeholder="Password" required="required">
</div>
<input type="submit" name="submit" value="Create account" />
</form>
</body>
</html>
登录.php
<?php
$email = sanitize_input($_POST['email']); //echo "Sanitized email: ".$email; echo "<br/>";
$password = $_POST['password']; //echo "Inputted password: ".$password; echo "<br/>";
if ((!isset($email)) || (!isset($password))) {
// VISITOR NEEDS TO ENTER AN EMAIL AND PASSWORD
//echo "Data not provided";
} else {
// CONNECT TO MYSQL
$mysql = mysqli_connect("localhost", "root", "root");
if(!$mysql) {
//echo "Cannot connect to PHPMyAdmin.";
exit;
} else {
}
}
// SELECT THE APPROPRIATE DATABASE
$selected = mysqli_select_db($mysql, "languageapp");
if(!$selected) {
//echo "Cannot select database.";
exit;
} else {
}
// GET THE USER'S UNIQUE SALT FROM THE DATABASE
$unique_salt = mysqli_query($mysql, "select uniqueSalt from user where email = '".$email."'");
$row = mysqli_fetch_array($unique_salt);
//echo "Salt: ".$row['uniqueSalt']; echo "<br/>";
// HASH THE PASSWORD
$iterations = 10;
$hashed_password = crypt($password,$row['uniqueSalt']);
for ($i = 0; $i < $iterations; ++$i)
{
$hashed_password = crypt($hashed_password . $password,$row['uniqueSalt']);
}
//echo "Password entered by user: ".$hashed_password; echo "<br/>";
$user_db_password = mysqli_query($mysql, "select password from user where email = '".$email."'");
$row = mysqli_fetch_array($user_db_password);
//echo "User's password: ".$row['password']; echo "<br/>";
// query the database to see if there is a record which matches
$query = "select count(*) from user where email = '".$email."' and password = '".$hashed_password."'";
$result = mysqli_query($mysql, $query);
if(!$result) {
//echo "Cannot run query.";
exit;
}
$row = mysqli_fetch_row($result);
$count = $row[0];
if ($count > 0) {
session_start();
$_SESSION['login'] = 1;
$_SESSION['email'] = $email;
$_SESSION['errors'] = "";
header("location:profile.php");
//echo "<h1>Login successful!</h1>";
//echo "<p>Welcome.</p>";
//echo "<p>This page is only visible when the correct details are provided.</p>";
} else {
session_start();
$_SESSION['login'] = '';
header("location:index.php");
//echo "<h1>Login unsuccessful!</h1>";
//echo "<p>The email and password combination entered was not recognized</p>";
}
// CLEAN THE INPUT
function sanitize_input($data)
{
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}
?>