I am new to PHP and am building a WordPress theme. I would like to add a variable in the functions.php and use it in single.php as an if statement. At present, my single.php has the following code -

  $prevPost = get_previous_post();
  $prevthumbnail = get_the_post_thumbnail($prevPost->ID, 'keepreading-thumb');

  if ( $prevPost ) : ?>
    <?php previous_post_link('%link',"$prevthumbnail"); ?>
    <h3><?php previous_post_link('%link'); ?></h3>
    <p><?php echo excerpt(25); ?></p>
  <?php endif; 

I would like to have the $prevPost and $prevthumbnail variables to be defined in functions.php and would like to use them in an "if statement" in single.php.

P.S - I am a newbie in coding and would appreciate it if you can give me an answer in detail. Thank you...


either use global variable in functions.php:

    global $prevPost;
    $prevPost = 10;

in single.php :

    global $prevPost;
     .. . . . Your code continues. .

Second method: define a function in functions.php and call that in single.php in functions.php :

    function func_prevPost(){
     $prevPost = 10;
     return $prevPost;

in single.php :

    // your code here
  • Thanks for the tip. I couldn't get the first one to work but the second one worked just fine. I am now using if(func_prevPost()){ and it works. But, I cannot get the thumbnail to show up. My actual code is $prevthumbnail = get_the_post_thumbnail($prevPost->ID, 'keepreading-thumb');. How can I add the $prevPost inside the above code. Also, how would I add it to the functions.php? Thank you... – Ajit Jun 21 '14 at 9:05

There are different ways to do that! This is easiest way:

Add your variables to a php files (e.g. config.php) and include it whenever you want to use its variables.


Another easy way is using $_GET or $_POST variables.


You can also define a global variable in functions.php.

global $my_var;

and then add global $my_var; before using it in single.php.


If I understand your question correctly, this code will only be used in single.php. Honestly I will stick with that code in single.php. Don't move it to functions.php and create a global varaible.

Globals might be useful at times, but I would advice you against adding variables to the global scope, unless you are using it itside a class or unless it is a really really necessarry. Globals in classes will only be accesible by that particular class.

Just a tip, if you ever add anything to the global scope, use names that no one will ever think of, never use names that will be easily replicated, as this might lead to a clash later on with plugins, even wordpress.

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