Session variables assignments

[race1]

Hello. I'd like to use some global variable for my site. I'm going to store this variable in session and all other modules/files should take variable from $_SESSION array.

There is special links, looking like this: <a href="...&tab=1">... and <a href="...&tab=2">. Then I set session variable in overrided tpl_index_default.php: $_SESSION['tab'] = $_GET['tab'] (not exactly, but it's simpler).

I use this variable in overrided categories.php. And in categories.php I see old session variable. I.e. if user click on first link, session variable will not be set at all. Then when user click on second link, categories.php says that session variable is "1". categories.php called earlier than tpl_index_default.php for sure!

So where I should place session variable assignment? I could do it in html_header.php but I can't override it and don't want to modify that file.

Thank you.

[race1]

Oh, I found solution. I should place tpl_header.php into /my_template/common. Then it works.