wp_set_post_categories( int $post_ID, array|int $post_categories = array(), bool $append = false )

Set categories for a post.

Description

If the post categories parameter is not set, then the default category is going used.

Parameters

$post_ID

(Optional) The Post ID. Does not default to the ID of the global $post. Default 0.

$post_categories

(Optional) List of categories or ID of category.

Default value: array()

$append

(Optional) If true, don't delete existing categories, just add on. If false, replace the categories with the new categories.

Default value: false

Return

(array|false|WP_Error) Array of term taxonomy IDs of affected categories. WP_Error or false on failure.

Source

File: wp-includes/post.php 

function wp_set_post_categories( $post_ID = 0, $post_categories = array(), $append = false ) {
	$post_ID = (int) $post_ID;
	$post_type = get_post_type( $post_ID );
	$post_status = get_post_status( $post_ID );
	// If $post_categories isn't already an array, make it one:
	$post_categories = (array) $post_categories;
	if ( empty( $post_categories ) ) {
		if ( 'post' == $post_type && 'auto-draft' != $post_status ) {
			$post_categories = array( get_option('default_category') );
			$append = false;
		} else {
			$post_categories = array();
		}
	} elseif ( 1 == count( $post_categories ) && '' == reset( $post_categories ) ) {
		return true;
	}

	return wp_set_post_terms( $post_ID, $post_categories, 'category', $append );
}

Expand Source Code View on GitHub

Related

Uses

Uses
Uses Description
wp-includes/option.php: get_option()

Retrieves an option value based on an option name.
wp-includes/post.php: wp_set_post_terms()

Set the terms for a post.
wp-includes/post.php: get_post_type()

Retrieves the post type of the current post or of a given post.
wp-includes/post.php: get_post_status()

Retrieve the post status based on the Post ID.

Changelog

Changelog
Version Description
WP-2.1.0 Introduced.