in_category( int|string|int[]|string[] $category, int|WP_Post $post = null ): bool

User Contributed Notes

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   Codex 9 years ago

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   Testing the current post outside the Loop
   During a request for an individual post (usually handled by the single.php template), you can test that post’s categories even before the Loop is begun.

   You could use this to switch templates like so:

   if ( in_category('fruit') ) {
   	include 'single-fruit.php';
   } elseif ( in_category('vegetables') ) {
   	include 'single-vegetables.php';
   } else {
   	// Continue with normal Loop
   	if ( have_posts() ) : while ( have_posts() ) : the_post();
   	// ...
   }

   (The Custom Post Templates Plugin allows for creation of templates for single posts. It also shows an example of how to add a template which is used for all posts in a given category, not just a single post. That example is commented out in the plugin by default but can be easily implemented by uncommenting the appropriate lines.)
2. Skip to note 6 content

   Codex 9 years ago

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   Testing the current post within the Loop
   in_category() is often used to take different actions within the Loop depending on the current post’s category, e.g.

   if ( in_category( 'pachyderms' )) {
   	// They have long trunks...
   } elseif ( in_category( array( 'Tropical Birds', 'small-mammals' ) )) {
   	// They are warm-blooded...
   } else {
   	// etc.
   }
3. Skip to note 7 content

   revive 3 years ago

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   To check whether a post is within a parent category or any of it’s subcategories:

   <?php
   /**
    * Tests if any of a post's assigned categories are descendants of target categories
    *
    * @param int|array $categories The target categories. Integer ID or array of integer IDs
    * @param int|object $_post The post. Omit to test the current post in the Loop or main query
    * @return bool True if at least 1 of the post's categories is a descendant of any of the target categories
    * @see get_term_by() You can get a category by name or slug, then pass ID to this function
    * @uses get_term_children() Passes $cats
    * @uses in_category() Passes $_post (can be empty)
    * @link originally at https://codex.wordpress.org/Function_Reference/in_category#Testing_if_a_post_is_in_a_descendant_category
    */
   
   if ( ! function_exists( 'wpdocs_post_is_in_a_subcategory' ) ) {
   function wpdocs_post_is_in_a_subcategory( $categories, $_post = null ) {
       foreach ( (array) $categories as $category ) {
           // get_term_children() only accepts integer ID
           $subcats = get_term_children( (int) $category, 'category' );
           if ( $subcats && in_category( $subcats, $_post ) )
               return true;
       }
       return false;
     }
   }
   ?>

   Use for checking if within a single cat:

   wpdocs_post_is_in_a_subcategory( 25 );

   Use for checking if within an array of parent categories, or any of their subcats:

   wpdocs_post_is_in_a_subcategory( array( 25, 28, 124, 297, 298, 299 ) );
4. Skip to note 8 content

   Iurié 9 months ago

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   It is not documented, but as I found in my tests, the in_category() function also accepts as a $category parameter a WP_Term object, returned for example by the get_term() function.

   • Interesting. Reviewing the chain of functions used, I can’t determine how/why this works.

     crstauf 9 months ago