I am using php and mysql on a Apache server in Linux. I have noticed in the book Php and Mysql, there is a "?" in certain spots that from what I gather is passing variables to the next page.  for example:

display_button("edit_category_form.php?catid=$catid", "edit-category", "Edit Category");

I am having trouble getting this to work and was wondering if this is a php setting or apache setting to enable the passing of variables to the next page.

The "?"  within the URL indicates that the following information is to be passed into the PHP as a  variable through the GET method - if you look at the URLs (locations lines) associated with this forum, you'll find it uses the same technique.  The display_button function that you have in your sample code is not part of the standard PHP function set, so I can't comment on why it's not working.

As of release 4 of PHP,  session fucntions such as session_start and  session_register allow you to register variables to a session so that they're maintained for you from one page to the next.  These routines also keep the sessions of different users apart so that (for example) orders don't get mixed up.  "Maintenance of state" is a major subject - really beyond the scope of a  quick answer on a form, and if you would like to studey this further I would direct you towards a good tutorial - for example in a book - or a training course that covers it.

Just to get you started, here's some PHP code that registers a session and
starts to make use of it too ...

<?php
 // Session demo - shopping cart

 session_start();

 //////////////// Brand new session - offer login

 if (! session_is_registered("active")) {
     session_register("active");
     $active = 1;
     $heading = "Welcome - please log in";
     $htmlsay = "Please enter your name <input name=whoareyou>";

 } else {

 //////////////// Name has been entered - store it

   if (! session_is_registered("uname")) {
       session_register("uname","cart");
       $uname = $whoareyou;
       $cart = array();

 }



I have ran into the same syntax where the "?" comes right after php in the parameters of the function. I was just curious as to if  I needed to turn on something in the php ini file to get the variable passing to work or if I can use the $HTTP_POST_VARS or something equivalent to pass the variable to the next page as opposed to retrieving it from the previous page.

The "?" straight after the URL (i.e. after the letters "php" in the case of a PHP page) signifies that the following information is to be sent on up to the server appended tot he URL - i.e. using the GET method, so it won't appear in the $HTTP_POST_VARS array - POST and GET are two different things.

In versions of PHP up to and including 4.1.x, the information afer the ? will appear in variables of the same name as the first word, content being the second word - for example
     .....php?fred=tom
will give you a variable called $fred with the value tom.

From versions 4.1.x up, you should use the $_GET array, so our example would set you an array element called $_GET["fred"] with a value of tom.  It is possible to change your php.ini file to still give you a variable with the same name as the field name on the form, but this is discouraged as it can lead to some weak security unless you're careful what you're doing!

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