Overriding functions?

Is there a way to overwrite a function like zen_get_buy_now_button? Do I copy the function into an extra file with the same name or a different name?

No there are no overrides for functions ... you would need to customize the original file ... save a copy of the original and your changed file for comparisons to future upgrades ...

Ajeh:

No there are no overrides for functions ...

Just like everything else in Zen Cart, where there's a will there's a way! I've used the method I'll describe for a while now, based on a post that I found once and can't resurrect. It's a bit convoluted, but it does provide an override mechanism.

The function zen_get_buy_now_button exists in functions_general.php.

Step 1: Copy /includes/init_includes/init_general_functions.php to /includes/init_includes/overrides/init_general_functions.php. Edit that file

<?php
/**
 * load the system wide functions
 * see {@link  http://www.zen-cart.com/wiki/index.php/Developers_API_Tutorials#InitSystem wikitutorials} for more details.
 *
 * @package initSystem
 * @copyright Copyright 2003-2005 Zen Cart Development Team
 * @copyright Portions Copyright 2003 osCommerce
 * @license http://www.zen-cart.com/license/2_0.txt GNU Public License V2.0
 * @version $Id: init_general_funcs.php 2845 2006-01-13 06:49:15Z drbyte $
 */
if (!defined('IS_ADMIN_FLAG')) {
  die('Illegal Access');
}
/**
 * General Functions
 */
require(DIR_WS_FUNCTIONS . 'overrides/functions_general.php');
/**
 * html_output functions (href_links, input types etc)
 */
require(DIR_WS_FUNCTIONS . 'html_output.php');
/**
 * basic email functions
 */
require(DIR_WS_FUNCTIONS . 'functions_email.php');
/**
 * EZ-Pages functions
 */
require(DIR_WS_FUNCTIONS . 'functions_ezpages.php');
/**
 * User Defined Functions
 */
include(DIR_WS_MODULES . 'extra_functions.php');
?>

Step 2: Create the directory /includes/functions/overrides. Copy /includes/functions/functions_general.php into that folder and edit it to your heart's content.

The other functions can be overridden in a similar manner.

Just remember that if you do that, your alterations are NOT multi-version friendly. So will absolutely require changes when a new version is released, to ensure compatibility.

And they're not compatible with other overrides done by the storeowner, if they've already created an override for init_general_functions

DrByte:

Just remember that if you do that, your alterations are NOT multi-version friendly. So will absolutely require changes when a new version is released, to ensure compatibility.

And they're not compatible with other overrides done by the storeowner, if they've already created an override for init_general_functions

DrByte, I'm not necessarily proposing that this approach be used for general add-on writers for the reasons you mentioned. I've found it useful in my one-off changes for my site(s) since the overrides that I've created are preserved on an upgrade.