Just a quick note - this time a year, for my time zone, that should return Anchorage (or something else in the AHST time zone) because of DST.

Assigned to the date/time guru.

Also does not return a time zone for Indian Standard Time: timezone_name_from_abbr('', 19800, 0)

In my testing, this is the list of offsets that do not work for PHP 5.2.6:

-34200, ckhst
-16200, ant
-12600, negt
-7200, addt
12600, irst
16200, aft
19800, ist
20700, npt
21600, aktst
23400, burt
28800, bnt
34200, cast
35100, cwst
37800, cst
39600, anat
41400, lhst
46800, anast
49500, chadt
50400, anast

Note some of the above abbreviations are obsolete, e.g. BURT has been replaced with MMT.  But the point is timezone_name_from_abbr() does not work for those offsets without an abbreviation.

Looking at http://cvs.php.net/viewvc.cgi/php-src/ext/date/lib/fallbackmap.h?revision=1.3&view=markup it appears to be a simple bug: lookups of the fallbackmap are not working for any of the time zones with non-integer offsets.  A more minor issue (in terms of affected population size) is that some valid offsets are missing from the fallbackmap.

The affected population sizes of the two issues may be similar after all: China standard time is missing from the fallbackmap (offset 8 hours, daylight saving time 0).

The originally filed reproduce code
var_dump( timezone_name_from_abbr('',-36000,1) );
and expected result 'Pacific/Honolulu' are not actually valid because Honolulu does not observe daylight saving time.  See comments above for what look like actual bugs.

I was able to resolve this by changing the fallbackmap from hours to minutes (the bug is apparently due to some issue with float vs. integer).  Also, this patch adds Caracas and Shanghai time (there are likely other missing time zones, however) and uses the new spelling for Calcutta (Kolkata).

Index: ext/date/lib/fallbackmap.h
===================================================================
RCS file: /repository/php-src/ext/date/lib/fallbackmap.h,v
retrieving revision 1.3
diff -u -p -r1.3 fallbackmap.h
--- ext/date/lib/fallbackmap.h	15 Oct 2005 18:14:40 -0000	1.3
+++ ext/date/lib/fallbackmap.h	8 May 2009 18:18:32 -0000
@@ -1,40 +1,42 @@
-	{ "sst",   0,  -11,  "Pacific/Apia" },
-	{ "hst",   0,  -10,  "Pacific/Honolulu" },
-	{ "akst",  0,   -9,  "America/Anchorage" },
-	{ "akdt",  1,   -8,  "America/Anchorage" },
-	{ "pst",   0,   -8,  "America/Los_Angeles" },
-	{ "pdt",   1,   -7,  "America/Los_Angeles" },
-	{ "mst",   0,   -7,  "America/Denver" },
-	{ "mdt",   1,   -6,  "America/Denver" },
-	{ "cst",   0,   -6,  "America/Chicago" },
-	{ "cdt",   1,   -5,  "America/Chicago" },
-	{ "est",   0,   -5,  "America/New_York" },
-	{ "edt",   1,   -4,  "America/New_York" },
-	{ "ast",   0,   -4,  "America/Halifax" },
-	{ "adt",   1,   -3,  "America/Halifax" },
-	{ "brt",   0,   -3,  "America/Sao_Paulo" },
-	{ "brst",  1,   -2,  "America/Sao_Paulo" },
-	{ "azost", 0,   -1,  "Atlantic/Azores" },
-	{ "azodt", 1,    0,  "Atlantic/Azores" },
-	{ "gmt",   0,    0,  "Europe/London" },
-	{ "bst",   1,    1,  "Europe/London" },
-	{ "cet",   0,    1,  "Europe/Paris" },
-	{ "cest",  1,    2,  "Europe/Paris" },
-	{ "eet",   0,    2,  "Europe/Helsinki" },
-	{ "eest",  1,    3,  "Europe/Helsinki" },
-	{ "msk",   0,    3,  "Europe/Moscow" },
-	{ "msd",   1,    4,  "Europe/Moscow" },
-	{ "gst",   0,    4,  "Asia/Dubai" },
-	{ "pkt",   0,    5,  "Asia/Karachi" },
-	{ "ist",   0,  5.5,  "Asia/Calcutta" },
-	{ "npt",   0, 5.75,  "Asia/Katmandu" },
-	{ "yekt",  1,    6,  "Asia/Yekaterinburg" },
-	{ "novst", 1,    7,  "Asia/Novosibirsk" },
-	{ "krat",  0,    7,  "Asia/Krasnoyarsk" },
-	{ "krast", 1,    8,  "Asia/Krasnoyarsk" },
-	{ "jst",   0,    9,  "Asia/Tokyo" },
-	{ "est",   0,   10,  "Australia/Melbourne" },
-	{ "cst",   1, 10.5,  "Australia/Adelaide" },
-	{ "est",   1,   11,  "Australia/Melbourne" },
-	{ "nzst",  0,   12,  "Pacific/Auckland" },
-	{ "nzdt",  1,   13,  "Pacific/Auckland" },
+	{ "sst",   0, -660, "Pacific/Apia" },
+	{ "hst",   0, -600, "Pacific/Honolulu" },
+	{ "akst",  0, -540, "America/Anchorage" },
+	{ "akdt",  1, -480, "America/Anchorage" },
+	{ "pst",   0, -480, "America/Los_Angeles" },
+	{ "pdt",   1, -420, "America/Los_Angeles" },
+	{ "mst",   0, -420, "America/Denver" },
+	{ "mdt",   1, -360, "America/Denver" },
+	{ "cst",   0, -360, "America/Chicago" },
+	{ "cdt",   1, -300, "America/Chicago" },
+	{ "est",   0, -300, "America/New_York" },
+	{ "vet",   0, -270, "America/Caracas" },
+	{ "edt",   1, -240, "America/New_York" },
+	{ "ast",   0, -240, "America/Halifax" },
+	{ "adt",   1, -180, "America/Halifax" },
+	{ "brt",   0, -180, "America/Sao_Paulo" },
+	{ "brst",  1, -120, "America/Sao_Paulo" },
+	{ "azost", 0,  -60, "Atlantic/Azores" },
+	{ "azodt", 1,    0, "Atlantic/Azores" },
+	{ "gmt",   0,    0, "Europe/London" },
+	{ "bst",   1,   60, "Europe/London" },
+	{ "cet",   0,   60, "Europe/Paris" },
+	{ "cest",  1,  120, "Europe/Paris" },
+	{ "eet",   0,  120, "Europe/Helsinki" },
+	{ "eest",  1,  180, "Europe/Helsinki" },
+	{ "msk",   0,  180, "Europe/Moscow" },
+	{ "msd",   1,  240, "Europe/Moscow" },
+	{ "gst",   0,  240, "Asia/Dubai" },
+	{ "pkt",   0,  300, "Asia/Karachi" },
+	{ "ist",   0,  330, "Asia/Kolkata" },
+	{ "npt",   0,  345, "Asia/Katmandu" },
+	{ "yekt",  1,  360, "Asia/Yekaterinburg" },
+	{ "novst", 1,  420, "Asia/Novosibirsk" },
+	{ "krat",  0,  420, "Asia/Krasnoyarsk" },
+	{ "cst",   0,  480, "Asia/Shanghai" },
+	{ "krast", 1,  480, "Asia/Krasnoyarsk" },
+	{ "jst",   0,  540, "Asia/Tokyo" },
+	{ "est",   0,  600, "Australia/Melbourne" },
+	{ "cst",   1,  630, "Australia/Adelaide" },
+	{ "est",   1,  660, "Australia/Melbourne" },
+	{ "nzst",  0,  720, "Pacific/Auckland" },
+	{ "nzdt",  1,  780, "Pacific/Auckland" },
Index: ext/date/lib/parse_date.c
===================================================================
RCS file: /repository/php-src/ext/date/lib/parse_date.c,v
retrieving revision 1.102
diff -u -p -r1.102 parse_date.c
--- ext/date/lib/parse_date.c	10 Mar 2009 23:39:11 -0000	1.102
+++ ext/date/lib/parse_date.c	8 May 2009 18:18:32 -0000
@@ -719,7 +719,7 @@ const static timelib_tz_lookup_table* zo
 	/* Still didn't find anything, let's find the zone solely based on
 	 * offset/isdst then */
 	for (fmp = timelib_timezone_fallbackmap; fmp->name; fmp++) {
-		if ((fmp->gmtoffset * 3600) == gmtoffset && fmp->type == isdst) {
+		if ((fmp->gmtoffset * 60) == gmtoffset && fmp->type == isdst) {
 			return fmp;
 		}
 	}
Index: ext/date/lib/parse_date.re
===================================================================
RCS file: /repository/php-src/ext/date/lib/parse_date.re,v
retrieving revision 1.92
diff -u -p -r1.92 parse_date.re
--- ext/date/lib/parse_date.re	18 Dec 2008 14:54:51 -0000	1.92
+++ ext/date/lib/parse_date.re	8 May 2009 18:18:32 -0000
@@ -717,7 +717,7 @@ const static timelib_tz_lookup_table* zo
 	/* Still didn't find anything, let's find the zone solely based on
 	 * offset/isdst then */
 	for (fmp = timelib_timezone_fallbackmap; fmp->name; fmp++) {
-		if ((fmp->gmtoffset * 3600) == gmtoffset && fmp->type == isdst) {
+		if ((fmp->gmtoffset * 60) == gmtoffset && fmp->type == isdst) {
 			return fmp;
 		}
 	}

I have the exact same problem and I found this bug entry thanks to someone at 
stackoverflow. Here was my original question: 
http://stackoverflow.com/questions/6180892/why-does-timezone-name-from-abbr-
return-an-empty-string

Test Code
------------------------------
$offset = -10; //UM10
echo timezone_name_from_abbr('', $offset * 3600, true); //empty string

Expected Result
------------------------------
Pacific/Honolulu

Actual result:
------------------------------
false

I am using PHP 5.3.0.

<?php $timezoneName = timezone_name_from_abbr("", 28800, false); ?>

Fatal error: Uncaught exception 'Exception' with message 'DateTimeZone::__construct() [<a href='datetimezone.--construct'>datetimezone.--construct</a>]: Unknown or bad timezone ()' in C:\ ... \test.php:46 Stack trace: #0 C:\ ... \test.php(46): DateTimeZone->__construct('') #1 {main} thrown in C:\ ... \test.php on line 46

I am using PHP 5.3.6 MSVC9 (Visual C++ 2008).

It is January 2013 and this bug is still around, even though 23 out of 24 current votes reproduced the bug!!

This issue isn't mentioned in the 5.5.10 changelog @ http://www.php.net/ChangeLog-5.php#5.5.10

Same for #45543

Following scripts shows the difference between 5.5.9 and 5.5.10: 
http://3v4l.org/1qPqL

Not sure which of these bugs causes this change, but I think it's worth mentioning in these changelog...

I use following code to get timezone name:  
$timezoneOffset = "05:30";
echo $timezone_name = timezone_name_from_abbr("",$timezoneOffset*3600,0);

but it's output is : Asia/Karachi
Expected output: Asia/Kolkata

This is still an issue as of PHP 5.5.27

PHP 5.5.27 (cli) (built: Jul 23 2015 00:21:59)
Copyright (c) 1997-2015 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2015 Zend Technologies


As this shows closed, what version is this supposedly fixed in?

> As this shows closed, what version is this supposedly fixed in?

This issue is fixed as of PHP 5.4.26 and 5.5.10. If you still
experience problems, please open a new ticket and provide a
reproduce script.