当我尝试登录时，它不允许我登录，但是当我取出它时，它允许我这样做，但即使我注销，它仍然允许我在页面上？
我知道有问题的领域是欢迎中的PHP代码.php
登录.php：
<html>
<body>
<form name="form1" method="post" action="connection.php">
<td colspan="3"><strong>Member Login </strong></td>
<td width="78">Username</td>
<td width="6">:</td>
<td width="294">
<input name="myusername" type="text" id="myusername">
</td>
Password:
<input name="mypassword" type="text" id="mypassword">
<input type="submit" name="Submit" value="Login">
</form>
</body>
</html>
连接.php：
<?php
ob_start();
$host="localhost"; // Host name
$username="root"; // Mysql username
$password=""; // Mysql password
$db_name="v2"; // Database name
$tbl_name="members"; // Table name
// Connect to server and select databse.
mysql_connect("$host", "$username", "$password")or die("cannot connect");
mysql_select_db("$db_name")or die("cannot select DB");
// Define $myusername and $mypassword
$myusername=$_POST['myusername'];
$mypassword=$_POST['mypassword'];
// To protect MySQL injection (more detail about MySQL injection)
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);
$sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword'";
$result=mysql_query($sql);
// Mysql_num_row is counting table row
$count=mysql_num_rows($result);
// If result matched $myusername and $mypassword, table row must be 1 row
if($count==1){
// Register $myusername, $mypassword and redirect to file "welcome.php"
$_SESSION["myusername"];
$_SESSION["mypassword"];
header("location:welcome.php");
}
else {
echo "Wrong Username or Password";
}
ob_end_flush();
?>
欢迎光临.php：
<?php
session_start();
if(!isset($_SESSION["myusername"])){
header("location:login.php");
}
?>
<html>
<body>
You have successfully logged in!
<br>
<a href="logout.php">Logout</a>
</body>
</html>
您应该尽量避免直接访问超级全局变量。您可以使用 php 'filter_input（INPUT_POST，'用户名'）;相反。还要记得加密您的密码。也许您在表中加密了密码，但在"选择"查询中无法解密......正确通过它。
我认为您需要更改为
// Register $myusername, $mypassword and redirect to file "welcome.php"
$_SESSION["myusername"]=$myusername;
$_SESSION["mypassword"]=$mypassword;
为了工作这个if(!isset($_SESSION["myusername"]))