timezone_identifiers_list - PHP code example

PHP Function Timezone Identifiers List

If you develop web applications that deal with date and time-related data, working with different timezones is a must. However, identifying and using the right timezone identifiers can be challenging for beginners. This article explores the php function timezone_identifiers_list, which allows you to fetch all of the time zone identifiers that are defined in PHP.

The php function timezone_identifiers_list() is an alias of the DateTimeZone::listIdentifiers() method, and it returns an indexed array containing all of the time zone identifiers defined in PHP. The function accepts two arguments: the datetimezone object and a two-letter ISO 3166-1 compatible country code. The function will return an indexed array on success and FALSE on failure.

In order to use the php function timezone_identifiers_list(), you must have a DateTimeZone class set up in your application. The first step is to define the DateTimeZone::PER_COUNTRY constant, which specifies the date and time zone in which the datetimezone object should be configured. Then, pass this value to the php function timezone_identifiers_list() in order to obtain a list of all the time zones configured for that region.

Once you have the indexed array of all the configured time zones, you can easily display a dropdown menu for your users to choose from. You can also use the indices to create your own custom time zone identifiers. For example, the indices for the Australian time zones are AU Central Standard Time, Australia/Darwin and AU Eastern Standard Time, while Melbourne is identified by the identifier AUS.

timezone_identifiers_list example

$continents = array( 'Africa', 'America', 'Antarctica', 'Arctic', 'Asia', 'Atlantic', 'Australia', 'Europe', 'Indian', 'Pacific' );

    // Load translations for continents and cities.     if ( ! $mo_loaded || $locale !== $locale_loaded ) {
        $locale_loaded = $locale ? $locale : get_locale();
        $mofile        = WP_LANG_DIR . '/continents-cities-' . $locale_loaded . '.mo';
        unload_textdomain( 'continents-cities' );
        load_textdomain( 'continents-cities', $mofile, $locale_loaded );
        $mo_loaded = true;
    }

    $tz_identifiers = timezone_identifiers_list();
    $zonen          = array();

    foreach ( $tz_identifiers as $zone ) {
        $zone = explode( '/', $zone );
        if ( ! in_array( $zone[0], $continents, true ) ) {
            continue;
        }

        // This determines what gets set and translated - we don't translate Etc/* strings here, they are done later.         $exists    = array(
            0 => ( isset( $zone[0] ) && $zone[0] ),

    $now = new DateTime( 'now', new DateTimeZone( $tzstring ) );
    $dst = (bool) $now->format( 'I' );

    if ( $dst ) {
        _e( 'This timezone is currently in daylight saving time.' );
    } else {
        _e( 'This timezone is currently in standard time.' );
    }
    ?> <br /> <?php     if ( in_array( $tzstring, timezone_identifiers_list( DateTimeZone::ALL_WITH_BC ), true ) ) {
        $transitions = timezone_transitions_get( timezone_open( $tzstring ), time() );

        // 0 index is the state at current time, 1 index is the next transition, if any.         if ( ! empty( $transitions[1] ) ) {
            echo ' ';
            $message = $transitions[1]['isdst'] ?
                /* translators: %s: Date and time. */
                __( 'Daylight saving time begins on: %s.' ) :
                /* translators: %s: Date and time. */
                __( 'Standard time begins on: %s.' );
            printf(

    $offset_or_tz = _x( '0', 'default GMT offset or timezone string' );
    if ( is_numeric( $offset_or_tz ) ) {
        $gmt_offset = $offset_or_tz;
    } elseif ( $offset_or_tz && in_array( $offset_or_tz, timezone_identifiers_list( DateTimeZone::ALL_WITH_BC ), true ) ) {
        $timezone_string = $offset_or_tz;
    }

    $defaults = array(
        'siteurl'                         => $guessurl,
        'home'                            => $guessurl,
        'blogname'                        => __( 'My Site' ),
        'blogdescription'                 => '',
        'users_can_register'              => 0,
        'admin_email'                     => 'you@example.com',
        /* translators: Default start of the week. 0 = Sunday, 1 = Monday. */

    public static function getSubscribedEvents()
    {
        return [KernelEvents::REQUEST => 'onKernelRequest'];
    }

    public function onKernelRequest(RequestEvent $event): void
    {
        $timezone = (string) $event->getRequest()->cookies->get(self::TIMEZONE_COOKIE);

        if (!$timezone || !\in_array($timezone, timezone_identifiers_list(), true) || $timezone === 'UTC') {
            // Default will be UTC @see https://symfony.com/doc/current/reference/configuration/twig.html#timezone             return;
        }

        $twig = $this->container->get('twig');

        if (!$twig->hasExtension(CoreExtension::class)) {
            return;
        }

        /** @var CoreExtension $coreExtension */

return (bool) preg_match($pattern, $str ?? '');
    }

    /** * Validates that the string is a valid timezone as per the * timezone_identifiers_list function. * * @see http://php.net/manual/en/datetimezone.listidentifiers.php */
    public function timezone(?string $str = null): bool
    {
        return in_array($str ?? '', timezone_identifiers_list(), true);
    }

    /** * Valid Base64 * * Tests a string for characters outside of the Base64 alphabet * as defined by RFC 2045 http://www.faqs.org/rfcs/rfc2045 */
    public function valid_base64(?string $str = null): bool
    {
        if ($str === null) {

if ( ! preg_match( '/(--|\.\.)/', $domain ) && preg_match( '|^([a-zA-Z0-9-\.])+$|', $domain ) ) {
                        $value[] = $domain;
                    }
                }
                if ( ! $value ) {
                    $value = '';
                }
            }
            break;

        case 'timezone_string':
            $allowed_zones = timezone_identifiers_list( DateTimeZone::ALL_WITH_BC );
            if ( ! in_array( $value, $allowed_zones, true ) && ! empty( $value ) ) {
                $error = __( 'The timezone you have entered is not valid. Please select a valid timezone.' );
            }
            break;

        case 'permalink_structure':
        case 'category_base':
        case 'tag_base':
            $value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', $value );
            if ( is_wp_error( $value ) ) {
                $error = $value->get_error_message();
            }