Your first reference to a session (usually session_start()) must come
before any html is sent to the browser. A common problem is to have some
white space before the <?php tag or after the ?> tag in a preceding file.
You can set up something like what you're working on using session
variables. Create random numbers and stick them in each form as a hidden
input with the name formId or something. Then register an array of used
formId's as a session variable. At the top of each script check if there's
a formId and if so see if it's in the used ids array. If so you can chuck
out the form input, if not, the form's ok, but add the new formId to the
used ids array.
This should at least keep someone from re-submitting a form in the same
session.
-Steve
On 2001.12.22 00:09:30 -0600 Andrew V. Romero wrote:
> I was wondering if there is a way to ensure that a form is only
> submitted once. I have a script that saves a lot of information to the
> disk and if the user uses the back button and then resubmits the form,
> it will cause major problems. I jave looked into using javascript to
> fix this, but it doesn't seem like there is an easy way using
> javascript. In the process of looking into this, someone recommended
> using a session variable. I have never used sesion variables, but tried
> a sample code in the documentation:
> <?php
> session_register ("count");
> $count++;
> ?>
> Hello visitor, you have seen this page <?php echo $count; ?> times.<p>
> <php?
> # the <?=SID?> is necessary to preserve the session id
> # in the case that the user has disabled cookies
> ?>
> To continue, <A HREF="nextpage.php?<?=SID?>">click here</A>
>
> but I get an error saying "Warning: Cannot send session cookie - headers
> already sent by (output started at
> c:\server\apache\htdocs\session.phtml:5)" and "Warning: Cannot send
> session cache limiter - headers already sent (output started at
> c:\server\apache\htdocs\session.phtml:5) in
> c:\server\apache\htdocs\session.phtml".
>
> So two questions, first is a sesssion variable the way to go in ensuring
> that the user doesn't use the back button to resubmit a form, and
> secondly why am I getting this errors when I just cut and paste the
> example code into a sample page?
>
> Thanks for any direction and help,
> Andrew V. Romero
>
>
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