Clearing the cookie programmatically - php

Question

I have a login page called signin.php where a user can enter an email and password. On clicking submit button, page directs to connection_validate.php. This page validates the user entered data with database. If it's a registered user, the page directs to calendar.php. If the entered data is incorrect, it should redirect to signin.php. If the entered data is incorrect, I have placed cookie like this:
//action to be done if e mail id and password matches with database records
if(mysql_num_rows($result)>0)
{
header('location:calendar.php');
}
//action to be done if e mail id and password does not matches with database records
else
{
setcookie('message','incorrect login data');
header('location:signin.php');
}
In signin.php, I have written the code for displaying an alert if login information is incorrect like this:
<?php
include("include/minfooter.php");
if(isset($_COOKIE["message"]))
{
if(!($_COOKIE["message"]==" "))
{
echo "<script>
alert('Incorrect login information');
</script>";
setcookie("message"," ",time()-3600);
}
}
?>
My issue is that alert is displaying each time when I load the signin page if I have entered a error login data once. If I press the back button from the calendar.php to signin.php also, alert starts showing. I understood that the problem is with cookie. Cookie has not been removed. How can I solve this issue?

Answer 1

Update your signin.php as follows
<?php
include("include/minfooter.php");
if (isset($_COOKIE["message"]))
{
echo "<script>
var delete_cookie = function(name) {
document.cookie = name + '=;expires=Thu, 01 Jan 1970 00:00:01 GMT;';
};
var msg = '" . $_COOKIE["message"] . "';
if (msg != '')
alert('Incorrect login information');
delete_cookie('message');
</script>";
}
?>

Answer 2

If you are using a session you can use the $_SESSION variable instead of a cookie value. Also you can not use setcookie() AFTER you have output content since setcookie() will send an HTTP header which must be sent prior to any content being sent.
session_start();
//action to be done if email id and password matches with database records
if (mysql_num_rows($result) > 0)
{
header('Location: calendar.php');
exit;
}
//action to be done if email id and password does not matches with database records
else
{
$_SESSION['message'] = 'incorrect login data';
header('Location: signin.php');
exit;
}
Then:
<?php
session_start();
include("include/minfooter.php");
if (!empty($_SESSION['message']))
{
echo "<script>alert('" . $_SESSION["message"] . "');</script>";
$_SESSION['message'] = '';
}
?>

Answer 3

Ok maybe is better to use session for that use a index ['messages'] on the $_SESSION array, then cleanup, the cookie should be used when you want reference some info after the user get out of your page. I made your code on using cookies, but consider using session:
<?php include("include/minfooter.php");
if(isset($_COOKIE["message"]) && !empty($_COOKIE["message"])
{
echo "<script>
var msg = '<?php echo $_COOKIE["message"];?>';
if (msg != "")
alert('Incorrect login information');
</script>";
unset($_COOKIE["message"]);
}
?>