A question about brower page lookup using PHP

[khovorka]

Hello,

I am starting to use php_gd2.dll for a project and
I am experiencing the following issue.

The image i am creating is written to a file using imagepng.
This is a dynamic chart.

However, if I make a change dynamically to my chart
the change isn't reflected in my page.

I needed to go to IE5 Browsers Tools->Internet Options->
Settings and then click on the option to :

check for a new version of stored pages: On every visit to the page.

We have people who use our site that are not all that computer
savy and so the would not even attempt to change this setting
and get frustrated and leave the site if I said you have to
go and do the above mentioned change.

Is there a way in PHP to make sure that this issue could be
fixed?

Thanks,
Kim Hovorka
[e-mail]

[wilsonodk]

I always use these 4 meta tags if I need a page to not be stored in cache...

<meta http-equiv="Pragma" content="no-cache">
<meta http-equiv="no-cache">
<meta http-equiv="Expires" content="-1">
<meta http-equiv="Cache-Control" content="no-cache">

Hope that helps.

[Roger_Ramjet]

Simplest fix is to turn off or override browser cacheing. IE will not reload from the server untill the local copy expires, and without expiry dates and modified dates in the stored copies, this would be never.

Use the following at the top of your page. Note that this code must be the first thing in the page

<?php		//index.php
//disable all browser caching MUST BE FIRST LINES WITH NO PRECEEDING SPACES ETC
// Date in the past
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");

// always modified
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");

// HTTP/1.1
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);

// HTTP/1.0
header("Pragma: no-cache");

// include neccessary files
	require_once './db.php';
	require_once './common.php';
	require_once './accesscontrol.php';
?>

Of course, people who already have a stored copy of your page are not going to get this. Even if they hit the refresh button to get your new page with its cache override, the old page will not be overwritten (no-cache) and still will not have expired(this is a bug in IE). They would need to clear their cache to get rid of your old pages, or keep on clicking refresh.

I'm sure there is a way of sending a header that forces a reload of your page, and if you use a short expiry date you will purge old copies.

Basically for dynamic web pages using the above script from the very beginning is a must. Even then, some proxy servers will ignore the headers and still cache your dynamic pages.