所以我正在学习如何为我正在制作的网站制作一个简单的登录系统，我得到这个错误。
注意:使用未定义的常量myusername -假设'myusername'在/home/dkitterm/public_html/index.php第4行
这是第3-6行。
session_start();
if(!session_is_registered(myusername)){
header("location: main_login.php");
}
这也是我的支票登录页面。
<?php
$host="localhost";
$username="dkitterm";
$password="";
$db_name="";
$tbl_name="members";
//connect to server and db
mysql_connect("$host", "$username", "$password") or die("Server Down");
mysql_select_db("$db_name") or die("cannot select DB");
//username and password sent from form
$myusername=$_POST['myusername'];
$mypassword=$_POST['mypassword'];
//debunk
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);
//encrypt password
$encrypted_mypassword=md5($mypassword);
$sql="SELECT * FROM members WHERE login='$myusername' and password='$encrypted_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, $mypassword and redirect to file "login_success.php"
session_register("myusername");
session_register("mypassword");
header("location: index.php");
}
else {
echo "Wrong Username or Password";
}
?>
@Col。Sharpanel说这是另一个更好的解决方案，因为你使用了一个贬值的函数。
session_start();
if(!isset($_SESSION['myusername'])){
header("location: main_login.php");
}
<?php
$host="localhost";
$username="dkitterm";
$password="";
$db_name="";
$tbl_name="members";
//connect to server and db
mysql_connect("$host", "$username", "$password") or die("Server Down");
mysql_select_db("$db_name") or die("cannot select DB");
//username and password sent from form
$myusername=$_POST['myusername'];
$mypassword=$_POST['mypassword'];
//debunk
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);
//encrypt password
$encrypted_mypassword=md5($mypassword);
$sql="SELECT * FROM members WHERE login='$myusername' and password='$encrypted_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 "login_success.php"
$_SESSION['myusername'] = $myusername;
//if you need to register the password do the same but for the password
header("location: index.php");
}
else {
echo "Wrong Username or Password";
}
?>
首先，你的支票页不能100%保护你，所以你需要
session_start();
if(!session_is_registered("myusername")){
header("location: main_login.php");
die();
}
并在myusername周围加上引号，否则它会将其视为常量而不是