Table of Contents
ADOdb Date/Time Library
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(). Since version 5.20.13, the future date cutoff is limited to 200 years by default. This value is controlled by a constant which may be modified for user requirement.
- Support for Daylight Savings Time may not be completely implemented, see below for how to write your own function.
- There may be conflicting functionality with the PHP Date Default Timezone Functionality
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 independent of the rest of ADOdb, and can be used as standalone code.
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.
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) */
Daylight Savings Time
ADOdb date/time library does not support daylight savings time but you can write your own function.
Future Date Cutoff
For security reasons, the maximum future date that can be generated is defaulted to 200 years in the future. This is controlled by the constant
ADODB_FUTURE_DATE_CUTOFF_YEARS which may be set as needed by the end user.
|adodb_time()||Returns the current time measured in the number of seconds since the Unix Epoch as a string|
|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()||Convert a timestamp to a formatted local date|
|adodb_last_date_status()||Returns the success of the last date conversion|
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/