wp_get_post_categories() WP 1.0

Retrieve the list of categories for a post.

Compatibility layer for themes and plugins. Also an easy layer of abstraction away from the complexity of the taxonomy layer.

No Hooks.

Return

Array/WP_Error. List of categories. If the $fields argument passed via $args is 'all' or 'all_with_object_id', an array of WP_Term objects will be returned. If $fields is 'ids', an array of category ids. If $fields is 'names', an array of category names. WP_Error object if 'category' taxonomy doesn't exist.

Usage

wp_get_post_categories( $post_id, $args );

$post_id(int)

The Post ID. Does not default to the ID of the global $post.
Default: 0

$args(array)

Category query parameters. See WP_Term_Query::__construct() for supported arguments.
Default: empty array

Code of wp get post categories: wp-includes/post.php ^{WP 5.2.1}

<?php
function wp_get_post_categories( $post_id = 0, $args = array() ) {
	$post_id = (int) $post_id;

	$defaults = array( 'fields' => 'ids' );
	$args     = wp_parse_args( $args, $defaults );

	$cats = wp_get_object_terms( $post_id, 'category', $args );
	return $cats;
}

Related Functions

From category: For posts