how to get current post id in wordpress code example

Example 1: wordpress get post id

// Retrieve the ID of the current item in the WordPress Loop.
get_the_ID()

Example 2: get_the_id wordpress

function get_the_ID() { // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.FunctionNameInvalid
    $post = get_post();
    return ! empty( $post ) ? $post->ID : false;
}

Example 3: wordpress get post by id

$post   = get_post( 123 ); // Where 123 is the ID
$output =  apply_filters( 'the_content', $post->post_content );