How to iterate through custom posts and add the title to an array

I am trying to query some custom posts so that I can iterate through them, extract the title of ecah and add the titles into an array. The reason I am doing this is so that I can then create a select field in woocommerce using the array contents to generate the options (haven’t done this bit yet)

Can anyone see where I’m going wrong with this snippet or provide any advice, I can’t get it to work. The site goes down and I get nothing in a var_dump

add_action('woocommerce_after_order_notes', 'custom_checkout_field');

function custom_checkout_field($checkout)

{

$args = array(
    'post_type'         => 'pickup-point',
    'posts_per_page'    => -1,
    'post_status'       => 'publish'
    );

// Custom query to pull in the pickup points.
$query = new WP_Query( $args );

// Check that we have query results.
if ( $query->have_posts() ) {


    $available_locations = [];

  while ( $query->have_posts() ) {

        $query->the_post();

        array_push($available_locations, the_title());

    }
}

var_dump ($available_locations);

}

// Restore original post data.
wp_reset_postdata();

I see two problems with the code you’ve written. The first one is that the_title() echos the post title although returning the title would be more appropriate in this context. Also wp_reset_postdata() should be after the while loop inside the if statement.

But as you mentioned that you only need the post titles, you can get them directly from the post objects from the query object without setting up the loop with have_posts() and the_post(). Like so,

add_action('woocommerce_after_order_notes', 'custom_checkout_field');
function custom_checkout_field($checkout) {

  $args = array(
    'post_type'              => 'pickup-point',
    'posts_per_page'         => -1,
    'post_status'            => 'publish',
    'no_found_rows'          => true, // pagination not needed
    'update_post_meta_cache' => false, // post meta not needed
    'update_post_term_cache' => false, // taxonomy terms not needed
  );
  $query = new WP_Query( $args );

  $titles = array_map( 'get_the_title', $query->posts );
  if ( $titles ) {
    // do something with $titles    
  }

}

I added couple of extra parameters to the query $args, which make the query a bit more efficient as only post titles are needed.