How to check is timezone identifier valid from code?

I'll try to explain what's the problem here.

According to list of supported timezones from PHP manual, I can see all valid TZ identifiers in PHP.

My first question is how to get that list from code but that's not what I really need.

My final goal is to write function isValidTimezoneId() that returns TRUE if timezone is valid, otherwise it should return FALSE.

function isValidTimezoneId($timezoneId) {  # ...function body...  return ?; # TRUE or FALSE  }

So, when I pass TZ identifier using $timezoneId (string) in function I need boolean result.

Well, what I have so far...

1) Solution using @ operator

First solution I've got is something like this:

function isValidTimezoneId($timezoneId) {  $savedZone = date_default_timezone_get(); # save current zone  $res = $savedZone == $timezoneId; # it's TRUE if param matches current zone  if (!$res) { # 0r...    @date_default_timezone_set($timezoneId); # try to set new timezone    $res = date_default_timezone_get() == $timezoneId; # it's true if new timezone set matches param string.    }  date_default_timezone_set($savedZone); # restore back old timezone  return $res; # set result  }

That works perfectly, but I want another solution (to avoid trying to set wrong timezone)

2) Solution using timezone_identifiers_list()

Then, I was trying to get list of valid timezone identifiers and check it against parameter using in_array() function. So I've tried to use timezone_identifiers_list(), but that was not so good because a lot of timezones was missing in array returned by this function (alias of DateTimeZone::listIdentifiers()). At first sight that was exactly what I was looking for.

function isValidTimezoneId($timezoneId) {  $zoneList = timezone_identifiers_list(); # list of (all) valid timezones  return in_array($timezoneId, $zoneList); # set result  }

This code looks nice and easy but than I've found that $zoneList array contains ~400 elements. According to my calculations it should return 550+ elements. 150+ elements are missing... So that's not good enough as solution for my problem.

3) Solution based on DateTimeZone::listAbbreviations()

This is last step on my way trying to find perfect solution. Using array returned by this method I can extract all timezone identifiers supported by PHP.

function createTZlist() {  $tza = DateTimeZone::listAbbreviations();  $tzlist = array();  foreach ($tza as $zone)    foreach ($zone as $item)       if (is_string($item['timezone_id']) && $item['timezone_id'] != '')        $tzlist[] = $item['timezone_id'];  $tzlist = array_unique($tzlist);  asort($tzlist);  return array_values($tzlist);  }

This function returns 563 elements (in Example #2 I've got just 407).

I've tried to find differences between those two arrays:

$a1 = timezone_identifiers_list();$a2 = createTZlist();print_r(array_values(array_diff($a2, $a1)));

Result is:

Array(    [0] => Africa/Asmera    [1] => Africa/Timbuktu    [2] => America/Argentina/ComodRivadavia    [3] => America/Atka    [4] => America/Buenos_Aires    [5] => America/Catamarca    [6] => America/Coral_Harbour    [7] => America/Cordoba    [8] => America/Ensenada    [9] => America/Fort_Wayne    [10] => America/Indianapolis    [11] => America/Jujuy    [12] => America/Knox_IN    [13] => America/Louisville    [14] => America/Mendoza    [15] => America/Porto_Acre    [16] => America/Rosario    [17] => America/Virgin    [18] => Asia/Ashkhabad    [19] => Asia/Calcutta    [20] => Asia/Chungking    [21] => Asia/Dacca    [22] => Asia/Istanbul    [23] => Asia/Katmandu    [24] => Asia/Macao    [25] => Asia/Saigon    [26] => Asia/Tel_Aviv    [27] => Asia/Thimbu    [28] => Asia/Ujung_Pandang    [29] => Asia/Ulan_Bator    [30] => Atlantic/Faeroe    [31] => Atlantic/Jan_Mayen    [32] => Australia/ACT    [33] => Australia/Canberra    [34] => Australia/LHI    [35] => Australia/NSW    [36] => Australia/North    [37] => Australia/Queensland    [38] => Australia/South    [39] => Australia/Tasmania    [40] => Australia/Victoria    [41] => Australia/West    [42] => Australia/Yancowinna    [43] => Brazil/Acre    [44] => Brazil/DeNoronha    [45] => Brazil/East    [46] => Brazil/West    [47] => CET    [48] => CST6CDT    [49] => Canada/Atlantic    [50] => Canada/Central    [51] => Canada/East-Saskatchewan    [52] => Canada/Eastern    [53] => Canada/Mountain    [54] => Canada/Newfoundland    [55] => Canada/Pacific    [56] => Canada/Saskatchewan    [57] => Canada/Yukon    [58] => Chile/Continental    [59] => Chile/EasterIsland    [60] => Cuba    [61] => EET    [62] => EST    [63] => EST5EDT    [64] => Egypt    [65] => Eire    [66] => Etc/GMT    [67] => Etc/GMT+0    [68] => Etc/GMT+1    [69] => Etc/GMT+10    [70] => Etc/GMT+11    [71] => Etc/GMT+12    [72] => Etc/GMT+2    [73] => Etc/GMT+3    [74] => Etc/GMT+4    [75] => Etc/GMT+5    [76] => Etc/GMT+6    [77] => Etc/GMT+7    [78] => Etc/GMT+8    [79] => Etc/GMT+9    [80] => Etc/GMT-0    [81] => Etc/GMT-1    [82] => Etc/GMT-10    [83] => Etc/GMT-11    [84] => Etc/GMT-12    [85] => Etc/GMT-13    [86] => Etc/GMT-14    [87] => Etc/GMT-2    [88] => Etc/GMT-3    [89] => Etc/GMT-4    [90] => Etc/GMT-5    [91] => Etc/GMT-6    [92] => Etc/GMT-7    [93] => Etc/GMT-8    [94] => Etc/GMT-9    [95] => Etc/GMT0    [96] => Etc/Greenwich    [97] => Etc/UCT    [98] => Etc/UTC    [99] => Etc/Universal    [100] => Etc/Zulu    [101] => Europe/Belfast    [102] => Europe/Nicosia    [103] => Europe/Tiraspol    [104] => Factory    [105] => GB    [106] => GB-Eire    [107] => GMT    [108] => GMT+0    [109] => GMT-0    [110] => GMT0    [111] => Greenwich    [112] => HST    [113] => Hongkong    [114] => Iceland    [115] => Iran    [116] => Israel    [117] => Jamaica    [118] => Japan    [119] => Kwajalein    [120] => Libya    [121] => MET    [122] => MST    [123] => MST7MDT    [124] => Mexico/BajaNorte    [125] => Mexico/BajaSur    [126] => Mexico/General    [127] => NZ    [128] => NZ-CHAT    [129] => Navajo    [130] => PRC    [131] => PST8PDT    [132] => Pacific/Ponape    [133] => Pacific/Samoa    [134] => Pacific/Truk    [135] => Pacific/Yap    [136] => Poland    [137] => Portugal    [138] => ROC    [139] => ROK    [140] => Singapore    [141] => Turkey    [142] => UCT    [143] => US/Alaska    [144] => US/Aleutian    [145] => US/Arizona    [146] => US/Central    [147] => US/East-Indiana    [148] => US/Eastern    [149] => US/Hawaii    [150] => US/Indiana-Starke    [151] => US/Michigan    [152] => US/Mountain    [153] => US/Pacific    [154] => US/Pacific-New    [155] => US/Samoa    [156] => Universal    [157] => W-SU    [158] => WET    [159] => Zulu)

This list contains all valid TZ identifiers that Example #2 failed to match.

There's four TZ identifiers more (part of $a1):

print_r(array_values(array_diff($a1, $a2)));

Output

Array(    [0] => America/Bahia_Banderas    [1] => Antarctica/Macquarie    [2] => Pacific/Chuuk    [3] => Pacific/Pohnpei)

So now, I have almost perfect solution...

function isValidTimezoneId($timezoneId) {  $zoneList = createTZlist(); # list of all valid timezones (last 4 are not included)  return in_array($timezoneId, $zoneList); # set result  }

That's my solution and I can use it. Of course, I use this function as part of class so I don't need to generate $zoneList on every methods call.

What I really need here?

I'm wondering, is there any easier (quicker) solution to get list of all valid timezone identifiers as array (I want to avoid extracting that list from DateTimeZone::listAbbreviations() if that's possible)? Or if you know another way how to check is timezone parameter valid, please let me know (I repeat, @ operator can't be part of solution).

P.S. If you need more details and examples, let me know. I guess you don't.

I'm using PHP 5.3.5 (think that's not important).

Update

Any part of code that throws exception on invalid timezone string (hidden using @ or caught using try..catch block) is not solution I'm looking for.