Retrieve meta field names for a post.

If there are no meta fields, then nothing (null) will be returned.

Signature

get_post_custom_keys( $post_id = 0 )
post_id
 (int) Optional. Post ID. Default is ID of the global $post.
Default: 0

Return

(array|null) Either array of the keys, or null if keys could not be retrieved.

Source

function get_post_custom_keys( $post_id = 0 ) {
	$custom = get_post_custom( $post_id );

	if ( !is_array($custom) )
		return;

	if ( $keys = array_keys($custom) )
		return $keys;
}
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