How to check is timezone identifier valid from code?

Question

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).

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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).

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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.

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Another update

I've put small bounty on this question!

Now I'm looking for the easiest way how to extract list of all timezone identifiers in PHP array.

Answer 1

Why not use @ operator? This code works pretty well, and you don't change default timezone:

function isValidTimezoneId($timezoneId) {     @$tz=timezone_open($timezoneId);     return $tz!==FALSE; } 

If you don't want @, you can do:

function isValidTimezoneId($timezoneId) {     try{         new DateTimeZone($timezoneId);     }catch(Exception $e){         return FALSE;     }     return TRUE; }