PHP Coding Tip: The print_r() Function

Here's a quick but extremely useful tip for PHP developers. When working on plugins or extensions for an existing framework, use the print_r() function on the API objects to find out what data structures they contain. Great PHP help tip.

This function is a big help for Joomla! development. There really isn't much documentation for Joomla! 1.5. The basic framework is there, but examples are extremely basic and don't have the information I would expect from a top-notch open source product (which Joomla! certainly is). This means that a lot of your coding will be a trial and error process.

You can speed up this process by using PHP's print_r() function. Print_r() basically takes a variable, even something complex like an array of arrays, and prints it to the screen in a humanly redable format, helping you figure out what data the object contains and how you can use it.

I found it very helpful when creating the Joomla! 1.5 version of the Ultimate Social Bookmarking Plugin. This was my first Joomla! 1.5 extension and I needed to know what data the $article variable contained. I wrapped it with a set of <pre></pre> tags to automatically format the data. Example:

echo '<pre>';
print_r($article);
echo '</pre>';

This simple chunk of PHP debugging code printed all of the information I needed to the screen. It told me exactly which fields existed within the $article object and what values they contained. I also learned that $article->alias only exists when the full content item is displayed, not on the homepage or blog/section/category listing pages. Here's an example output of the above code (with actual data values removed):

stdClass Object
(
[id] => 0
[title] => title
[alias] => alias
[title_alias] => 
[introtext] => intro text
[state] => 0
[sectionid] => 0
[mask] => 0
[catid] => 0
[created] => date
[created_by] => 0
[created_by_alias] => 
[modified] => date
[modified_by] => 0
[checked_out] => 0
[checked_out_time] => date
[publish_up] => date
[publish_down] => Never
[images] => 
[urls] => 
[attribs] => atts
[version] => 0
[parentid] => 0
[ordering] => 0
[metakey] => 
[metadesc] => 
[access] => 0
[hits] => 0
[metadata] => 
[author] => author
[usertype] => permissions
[category] => cat
[section] => sec
[slug] => slug
[catslug] => catslug
[groups] => groups
[sec_pub] => 0
[cat_pub] => 0
[sec_access] => 0
[cat_access] => 0
[rating_count] => 0
[rating] => 0
[text] => main article text
[parameters] => JParameter Object
(
[_raw] => show_noauth=0
show_title=1
link_titles=0
show_intro=1
show_section=0
link_section=0
show_category=0
link_category=0
show_author=0
show_create_date=1
show_modify_date=0
show_item_navigation=0
show_readmore=1
show_vote=0
show_icons=1
show_pdf_icon=0
show_print_icon=0
show_email_icon=0
show_hits=0
feed_summary=0
[_xml] => 
[_elements] => Array
(
)
[_elementPath] => Array
(
[0] => /path
)
[_defaultNameSpace] => _default
[_registry] => Array
(
[_default] => Array
(
[data] => stdClass Object
(
[show_noauth] => 0
[show_title] => 0
[link_titles] => 0
[show_intro] => 10
[show_section] => 0
[link_section] => 0
[show_category] => 0
[link_category] => 0
[show_author] => 0
[show_create_date] => 0
[show_modify_date] => 0
[show_item_navigation] => 0
[show_readmore] => 0
[show_vote] => 0
[show_icons] => 0
[show_pdf_icon] => 0
[show_print_icon] => 0
[show_email_icon] => 0
[show_hits] => 0
[feed_summary] => 0
[show_description] => 0
[show_description_image] => 0
[num_leading_articles] => 0
[num_intro_articles] => 0
[num_columns] => 0
[num_links] => 0
[show_pagination] => 0
[show_pagination_results] => 0
[show_feed_link] => 0
[html_title] => title
[robots] => index, follow
[show_page_title] => 0
[menu_image] => 0
[secure] => 0
[page_title] => title
[page_description] => description
[popup] => 0
)
)
)
[_errors] => Array
(
)
)
[readmore_link] => /link.html
)

Article by P.J. Swesey Open source software news and directory of open source software.

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Overall, PHP's print_r() function is awesome for debugging and development when you are working with objects that you just don't know enough about. It saves a lot of time and frustration when trying to code in a new environment. Definitely a helpful function.