Redirect Members Directory To Login Page For Non Logged in Users.

yzc_redirect_members_directory_to_login_page.php

<?php

/**
* Redirect Members Directory To Login Page For Non Logged in Users.
*/
function yzc_redirect_members_directory_to_login_page() {
    if ( ! is_user_logged_in() && bp_is_members_directory() ) {
        $redirect_url = yz_get_login_page_url();
        wp_redirect( $redirect_url );
        exit();
    }
}
add_action( 'template_redirect', 'yzc_redirect_members_directory_to_login_page' );