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Table of Contents
ADOdb Date/Time Libaray
- Support for Daylight Savings Time may not be completely implemented
- There may be conflicting functionality with the PHP Date Default Timezone Functionality
Introduction
PHP native date functions use integer timestamps for computations. Because of this, dates are restricted to the years 1901-2038 on Unix and 1970-2038 on Windows due to integer overflow for dates beyond those years. This library overcomes these limitations by replacing the native function's signed integers (normally 32-bits) with PHP floating point numbers (normally 64-bits).
Dates from 100 A.D. to 3000 A.D. and later have been tested. The minimum is 100 A.D. as <100 will invoke the 2 ⇒ 4 digit year conversion. The maximum is billions of years in the future, but this is a theoretical limit as the computation of that year would take too long with the current implementation of adodb_mktime().
Functions Replaced
This library replaces native functions as follows:
getdate() with adodb_getdate() date() with adodb_date() gmdate() with adodb_gmdate() mktime() with adodb_mktime() gmmktime() with adodb_gmmktime() strftime() with adodb_strftime() strftime() with adodb_gmstrftime()
The parameters are identical, except that adodb_date() accepts a subset of date()'s field formats. Mktime() will convert from local time to GMT, and date() will convert from GMT to local time, but daylight savings is
not handled currently.
This library is independant of the rest of ADOdb, and can be used as standalone code.
Performance
For high speed, this library uses the native date functions where possible, and only switches to PHP code when the dates fall outside the 32-bit signed integer range.
Gregorian Correction
Pope Gregory shortened October of A.D. 1582 by ten days. Thursday, October 4, 1582 (Julian) was followed immediately by Friday, October 15, 1582 (Gregorian).
This is handled correctly, so:
$t = adodb_mktime(0,0,0,10,15,1582) - adodb_mktime(0,0,0,10,4,1582) print $t; /* prints 24 * 3600 (1 day) */
Function Descriptions
| Function | Description |
|---|---|
| adodb_time() | Returns the current time measured in the number of seconds since the Unix Epoch |
| adodb_getdate() | Returns an array containing date information |
| adodb_date() | Convert a timestamp to a formatted local date |
| adodb_date2() | Same as adodb_date, but 2nd parameter accepts iso date |
| adodb_gmdate() | Convert a timestamp to a formatted GMT date |
| adodb_mktime( | Converts a local date to a unix timestamp |
| adodb_gmmktime() | Converts a gmt date to a unix timestamp |
| adodb_gmstrftime() | Convert a timestamp to a formatted GMT date |
| adodb_strftime($fmt, $timestamp = false) | Convert a timestamp to a formatted local date. Internally converts $fmt into adodb_date format, then echo result. For best results, you can define the local date format yourself. Define a global variable $ADODB_DATE_LOCALE which is an array, 1st element is date format using adodb_date syntax, and 2nd element is the time format, also in adodb_date syntax e.g. $ADODB_DATE_LOCALE = array('d/m/Y','H:i:s'); Supported format codes:%a - abbreviated weekday name according to the current locale %A - full weekday name according to the current locale %b - abbreviated month name according to the current locale %B - full month name according to the current locale %c - preferred date and time representation for the current locale %d - day of the month as a decimal number (range 01 to 31) %D - same as %m/%d/%y %e - day of the month as a decimal number, a single digit is preceded by a space (range ' 1' to '31') %h - same as %b %H - hour as a decimal number using a 24-hour clock (range 00 to 23) %I - hour as a decimal number using a 12-hour clock (range 01 to 12) %m - month as a decimal number (range 01 to 12) %M - minute as a decimal number %n - newline character %p - either `am' or `pm' according to the given time value, or the corresponding strings for the current locale %r - time in a.m. and p.m. notation %R - time in 24 hour notation %S - second as a decimal number %t - tab character %T - current time, equal to %H:%M:%S %x - preferred date representation for the current locale without the time %X - preferred time representation for the current locale without the date %y - year as a decimal number without a century (range 00 to 99) %Y - year as a decimal number including the century %Z - time zone or name or abbreviation %% - a literal `%' character Unsupported codes: %C - century number (the year divided by 100 and truncated to an integer, range 00 to 99)
%g - like %G, but without the century.
%G - The 4-digit year corresponding to the ISO week number (see %V).
This has the same format and value as %Y, except that if the ISO week number belongs
to the previous or next year, that year is used instead.
%j - day of the year as a decimal number (range 001 to 366)
%u - weekday as a decimal number [1,7], with 1 representing Monday
%U - week number of the current year as a decimal number, starting
with the first Sunday as the first day of the first week
%V - The ISO 8601:1988 week number of the current year as a decimal number,
range 01 to 53, where week 1 is the first week that has at least 4 days in the
current year, and with Monday as the first day of the week. (Use %G or %g for
the year component that corresponds to the week number for the specified timestamp.)
%w - day of the week as a decimal, Sunday being 0
%W - week number of the current year as a decimal number, starting with the
first Monday as the first day of the first week
|
Notes
Useful url for generating test timestamps
Possible future optimizations include
- Using an algorithm similar to Plauger's in “The Standard C Library” (page 428, xttotm.c _Ttotm() function). Plauger's algorithm will not work outside 32-bit signed range, so i decided not to implement it.
- Implement daylight savings, which looks awfully complicated, see http://webexhibits.org/daylightsaving/