Show Modified Date on Product Pages

How would I go about changing the information shown at the bottom of the product pages to a modified date, rather than the date added.

eg
Currently: This product was added to our catalog on Wednesday 30 January, 2013
Preferred: This product was last updated on Thursday 11 July 2013.

I know the field "products_last_modified" is available in the database, but my php/zencart skills just aren't up to the task of dealing with the null values that are present if the product has never been updated. Otherwise I think I could hack together a solution.

Any help would be greatly appreciated.

I would fetch both the date-added and last-modified from the db, then check for last-modified being null and substitute date-added in that case, to send to output.

You could customize the file:
/includes/templates/template_default/templates/tpl_product_info_display.php

and using your templates and overrides, customize the code:

    if ($flag_show_product_info_date_added == 1) {
?>
      <p id="productDateAdded" class="productGeneral centeredContent"><?php echo sprintf(TEXT_DATE_ADDED, zen_date_long($products_date_added)); ?></p>
<?php
    } // $flag_show_product_info_date_added

and change it by adding the code in RED:

    if ($flag_show_product_info_date_added == 1) {
?>
[B]<?
define('TEXT_DATE_MODIFIED', 'This product was last updated on %s');
$chk_date_added = zen_products_lookup((int)$_GET['products_id'], 'products_date_added');
$chk_date_modified = zen_products_lookup((int)$_GET['products_id'], 'products_last_modified');
if ($chk_date_modified <= $chk_date_added) {
?>
[/B]      <p id="productDateAdded" class="productGeneral centeredContent"><?php echo sprintf(TEXT_DATE_ADDED, zen_date_long($products_date_added)); ?></p>
[B]<?php } else { ?>[/B]
[B]      <p id="productDateAdded" class="productGeneral centeredContent"><?php echo sprintf(TEXT_DATE_MODIFIED, zen_date_long($chk_date_modified)); ?></p>
<?php } ?>
[/B]<?php
    } // $flag_show_product_info_date_added

then change your language file, again using your templates and overrides for the DEFINE for TEXT_DATE_ADDED to alter the text on how it reads ...

Ajeh:

You could customize the file:
/includes/templates/template_default/templates/tpl_product_info_display.php

Thanks for this, I will give it a try. Much appreciated.