# Zend_Date API Overview

While the Zend_Date API remains simplistic and unitary, its design remains flexible and powerful through the rich permutations of operations and operands.

## Zend_Date Options

### Selecting the Date Format Type

Several methods use date format strings, in a way similar to PHP's date(). If you are more comfortable with PHP's date format specifier than with ISO format specifiers, then you can use Zend_Date::setOptions(array('format_type' => 'php')). Afterward, use PHP's date format specifiers for all functions which accept a `$format` parameter. Use Zend_Date::setOptions(array('format_type' => 'iso')) to switch back to the default mode of supporting only ISO date format tokens. For a list of supported format codes, see Self-Defined OUTPUT Formats Using PHP's date() Format Specifiers

### DST and Date Math

When dates are manipulated, sometimes they cross over a DST change, normally resulting in the date losing or gaining an hour. For exmaple, when adding months to a date before a DST change, if the resulting date is after the DST change, then the resulting date will appear to lose or gain an hour, resulting in the time value of the date changing. For boundary dates, such as midnight of the first or last day of a month, adding enough months to cross a date boundary results in the date losing an hour and becoming the last hour of the preceding month, giving the appearance of an "off by 1" error. To avoid this situation, the DST change ignored by using the fix_dst option. When crossing the Summer or Winter DST boundary, normally an hour is substracted or added depending on the date. For example, date math crossing the Spring DST leads to a date having a day value one less than expected, if the time part of the date was originally 00:00:00. Since Zend_Date is based on timestamps, and not calendar dates with a time component, the timestamp loses an hour, resulting in the date having a calendar day value one less than expected. To prevent such problems use the option fix_dst, which defaults to `TRUE`, causing DST to have no effect on date "math" (addMonth(), subMonth()). Use Zend_Date::setOptions(array('fix_dst' => false)) to enable the subtraction or addition of the DST adjustment when performing date "math".

If your actual timezone within the instance of Zend_Date is set to UTC or GMT the option 'fix_dst' will not be used because these two timezones do not work with DST. When you change the timezone for this instance again to a timezone which is not UTC or GMT the previous set 'fix_dst' option will be used again for date "math".

### Month Calculations

When adding or substracting months from an existing date, the resulting value for the day of the month might be unexpected, if the original date fell on a day close to the end of the month. For example, when adding one month to January 31st, people familiar with SQL will expect February 28th as the result. On the other side, people familiar with Excel and OpenOffice will expect March 3rd as the result. The problem only occurs, if the resulting month does not have the day, which is set in the original date. For Zend Framework developers, the desired behavior is selectable using the extend_month option to choose either the SQL behaviour, if set to `FALSE`, or the spreadsheet behaviour when set to `TRUE`. The default behaviour for extend_month is `FALSE`, providing behavior compatible to SQL. By default, Zend_Date computes month calculations by truncating dates to the end of the month (if necessary), without wrapping into the next month when the original date designates a day of the month exceeding the number of days in the resulting month. Use Zend_Date::setOptions(array('extend_month' => true)) to make month calculations work like popular spreadsheet programs.

### Speed up Date Localization and Normalization with Zend_Cache

You can speed up Zend_Date by using an Zend_Cache adapter. This speeds up all methods of Zend_Date when you are using localized data. For example all methods which accept `Zend_Date::DATE` and `Zend_Date::TIME` constants would benefit from this. To set an Zend_Cache adapter to Zend_Date just use Zend_Date::setOptions(array('cache' => $adapter)).

### Receiving Syncronised Timestamps with Zend_TimeSync

Normally the clocks from servers and computers differ from each other. Zend_Date is able to handle such problems with the help of Zend_TimeSync. You can set a timeserver with Zend_Date::setOptions(array('timesync' => $timeserver)) which will set the offset between the own actual timestamp and the real actual timestamp for all instances of Zend_Date. Using this option does not change the timestamp of existing instances. So best usage is to set it within the bootstrap file.

## Working with Date Values

Once input has been normalized via the creation of a Zend_Date object, it will have an associated timezone, but an internal representation using standard UNIX timestamps. In order for a date to be rendered in a localized manner, a timezone must be known first. The default timezone is always GMT or UTC. To examine an object's timezone use getTimeZone(). To change an object's timezone, use setTimeZone(). All manipulations of these objects are assumed to be relative to this timezone.

Beware of mixing and matching operations with date parts between date objects for different timezones, which generally produce undesireable results, unless the manipulations are only related to the timestamp. Operating on Zend_Date objects having different timezones generally works, except as just noted, since dates are normalized to UNIX timestamps on instantiation of Zend_Date.

Most methods expect a constant selecting the desired `$part` of a date, such as `Zend_Date::HOUR`. These constants are valid for all of the functions below. A list of all available constants is provided in list of all constants. If no `$part` is specified, then `Zend_Date::TIMESTAMP` is assumed. Alternatively, a user-specified format may be used for `$part`, using the same underlying mechanism and format codes as Zend_Locale_Format::getDate(). If a date object is constructed using an obviously invalid date (e.g. a month number greater than 12), then Zend_Date will throw an exception, unless no specific date format has been selected -i.e. `$part` is either `NULL` or `Zend_Date::DATES` (a "loose" format).

User-Specified Input Date Format

    $date1 = new Zend_Date('Feb 31, 2007', null, 'en_US');
    echo $date1, "\n"; // outputs "Mar 3, 2007 12:00:00 AM"

    $date2 = new Zend_Date('Feb 31, 2007', Zend_Date::DATES, 'en_US');
    echo $date2, "\n"; // outputs "Mar 3, 2007 12:00:00 AM"

    // strictly restricts interpretation to specified format
    $date3 = new Zend_Date('Feb 31, 2007', 'MM.dd.yyyy');
    echo $date3, "\n"; // outputs "Mar 3, 2007 12:00:00 AM"

If the optional `$locale` parameter is provided, then the `$locale` disambiguates the `$date` operand by replacing month and weekday names for string `$date` operands, and even parsing date strings expressed according to the conventions of that locale (see Zend_Locale_Format::getDate()). The automatic normalization of localized `$date` operands of a string type occurs when `$part` is one of the `Zend_Date::DATE`* or `Zend_Date::TIME`* constants. The locale identifies which language should be used to parse month names and weekday names, if the `$date` is a string containing a date. If there is no `$date` input parameter, then the `$locale` parameter specifies the locale to use for localizing output (e.g. the date format for a string representation). Note that the `$date` input parameter might actually have a type name instead (e.g. `$hour` for addHour()), although that does not prevent the use of Zend_Date objects as arguments for that parameter. If no `$locale` was specified, then the locale of the current object is used to interpret `$date`, or select the localized format for output.

Since Zend Framework 1.7.0 Zend_Date does also support the usage of an application wide locale. You can simply set a Zend_Locale instance to the registry like shown below. With this notation you can forget about setting the locale manually with each instance when you want to use the same locale multiple times.

    // in your bootstrap file
    $locale = new Zend_Locale('de_AT');
    Zend_Registry::set('Zend_Locale', $locale);

    // somewhere in your application
    $date = new Zend_Date('31.Feb.2007');

## Basic Zend_Date Operations Common to Many Date Parts

The methods add(), sub(), compare(), get(), and set() operate generically on dates. In each case, the operation is performed on the date held in the instance object. The `$date` operand is required for all of these methods, except get(), and may be a Zend_Date instance object, a numeric string, or an integer. These methods assume `$date` is a timestamp, if it is not an object. However, the `$part` operand controls which logical part of the two dates are operated on, allowing operations on parts of the object's date, such as year or minute, even when `$date` contains a long form date string, such as, "December 31, 2007 23:59:59". The result of the operation changes the date in the object, except for compare(), and get().

Operating on Parts of Dates

    $date = new Zend_Date(); // $date's timestamp === time()

    // changes $date by adding 12 hours
    $date->add('12', Zend_Date::HOUR);
    print $date;

Convenience methods exist for each combination of the basic operations and several common date parts as shown in the tables below. These convenience methods help us lazy programmers avoid having to type out the date part constants when using the general methods above. Conveniently, they are named by combining a prefix (name of a basic operation) with a suffix (type of date part), such as addYear(). In the list below, all combinations of "Date Parts" and "Basic Operations" exist. For example, the operation "add" exists for each of these date parts, including addDay(), addYear(), etc.

These convenience methods have the same equivalent functionality as the basic operation methods, but expect string and integer `$date` operands containing only the values representing the type indicated by the suffix of the convenience method. Thus, the names of these methods (e.g. "Year" or "Minute") identify the units of the `$date` operand, when `$date` is a string or integer.

### List of Date Parts

Date Parts

Date Part | Explanation
--- | ---
Timestamp | UNIX timestamp, expressed in seconds elapsed since January 1st, 1970 00:00:00 GMT.
Year | Gregorian calendar year (e.g. 2006)
Month | Gregorian calendar month (1-12, localized names supported)
24 hour clock | Hours of the day (0-23) denote the hours elapsed, since the start of the day.
minute | Minutes of the hour (0-59) denote minutes elapsed, since the start of the hour.
Second | Seconds of the minute (0-59) denote the elapsed seconds, since the start of the minute.
millisecond | Milliseconds denote thousandths of a second (0-999). Zend_Date supports two additional methods for working with time units smaller than seconds. By default, Zend_Date instances use a precision defaulting to milliseconds, as seen using getFractionalPrecision(). To change the precision use setFractionalPrecision($precision). However, precision is limited practically to microseconds, since Zend_Date uses microtime().
Day | `Zend_Date::DAY_SHORT` is extracted from `$date` if the `$date` operand is an instance of Zend_Date or a numeric string. Otherwise, an attempt is made to extract the day according to the conventions documented for these constants: `Zend_Date::WEEKDAY_NARROW`, `Zend_Date::WEEKDAY_NAME`, `Zend_Date::WEEKDAY_SHORT`, `Zend_Date::WEEKDAY` (Gregorian calendar assumed)
Week | `Zend_Date::WEEK` is extracted from `$date` if the `$date` operand is an instance of Zend_Date or a numeric string. Otherwise an exception is raised. (Gregorian calendar assumed)
Date | `Zend_Date::DAY_MEDIUM` is extracted from `$date` if the `$date` operand is an instance of Zend_Date. Otherwise, an attempt is made to normalize the `$date` string into a `Zend_Date::DATE_MEDIUM` formatted date. The format of `Zend_Date::DAY_MEDIUM` depends on the object's locale.
Weekday | Weekdays are represented numerically as 0 (for Sunday) through 6 (for Saturday). `Zend_Date::WEEKDAY_DIGIT` is extracted from `$date`, if the `$date` operand is an instance of Zend_Date or a numeric string. Otherwise, an attempt is made to extract the day according to the conventions documented for these constants: `Zend_Date::WEEKDAY_NARROW`, `Zend_Date::WEEKDAY_NAME`, `Zend_Date::WEEKDAY_SHORT`, `Zend_Date::WEEKDAY` (Gregorian calendar assumed)
DayOfYear | In Zend_Date, the day of the year represents the number of calendar days elapsed since the start of the year (0-365). As with other units above, fractions are rounded down to the nearest whole number. (Gregorian calendar assumed)
Arpa | Arpa dates (i.e. RFC 822 formatted dates) are supported. Output uses either a "GMT" or "Local differential hours+min" format (see section 5 of RFC 822). Before PHP 5.2.2, using the `DATE_RFC822` constant with PHP date functions sometimes produces incorrect results. Zend_Date's results are correct. Example: Mon, 31 Dec 06 23:59:59 GMT
Iso | Only complete ISO 8601 dates are supported for output. Example: 2009-02-14T00:31:30+01:00

### List of Date Operations

The basic operations below can be used instead of the convenience operations for specific date parts, if the appropriate constant is used for the `$part` parameter.

Basic Operations

Basic Operation | Explanation
--- | ---
get() | get($part = null, $locale = null) Use get($part) to retrieve the date `$part` of this object's date localized to `$locale` as a formatted string or integer. When using the BCMath extension, numeric strings might be returned instead of integers for large values. Behaviour of get() Unlike get(), the other get*() convenience methods only return instances of Zend_Date containing a date representing the selected or computed date or time.
set() | set($date, $part = null, $locale = null) Sets the `$part` of the current object to the corresponding value for that part found in the input `$date` having a locale `$locale`.
add() | add($date, $part = null, $locale = null) Adds the `$part` of `$date` having a locale `$locale` to the current object's date.
sub() | sub($date, $part = null, $locale = null) Subtracts the `$part` of `$date` having a locale `$locale` from the current object's date.
copyPart() | copyPart($part, $locale = null) Returns a cloned object, with only `$part` of the object's date copied to the clone, with the clone have its locale arbitrarily set to `$locale` (if specified).
compare() | compare($date, $part = null, $locale = null) compares `$part` of `$date` to this object's timestamp, returning 0 if they are equal, 1 if this object's part was more recent than `$date`'s part, otherwise -1.

## Comparing Dates

The following basic operations do not have corresponding convenience methods for the date parts listed in Zend_Date API Overview.

Date Comparison Methods

Method | Explanation
--- | ---
equals() | equals($date, $part = null, $locale = null) returns `TRUE`, if `$part` of `$date` having locale `$locale` is the same as this object's date `$part`, otherwise `FALSE`
isEarlier() | isEarlier($date, $part = null, $locale = null) returns `TRUE`, if `$part` of this object's date is earlier than `$part` of `$date` having a locale `$locale`
isLater() | isLater($date, $part = null, $locale = null) returns `TRUE`, if `$part` of this object's date is later than `$part` of `$date` having a locale `$locale`
isToday() | isToday() Tests if today's year, month, and day match this object's date value, using this object's timezone.
isTomorrow() | isTomorrow() Tests if tomorrow's year, month, and day match this object's date value, using this object's timezone.
isYesterday() | isYesterday() Tests if yesterday's year, month, and day match this object's date value, using this object's timezone.
isLeapYear() | isLeapYear() Use isLeapYear() to determine if the current object is a leap year, or use Zend_Date::checkLeapYear($year) to check `$year`, which can be a string, integer, or instance of Zend_Date. Is the year a leap year?
isDate() | isDate($date, $format = null, $locale = null) This method checks if a given date is a real date and returns `TRUE` if all checks are ok. It works like PHP's checkdate() function but can also check for localized month names and for dates extending the range of checkdate()

## Getting Dates and Date Parts

Several methods support retrieving values related to a Zend_Date instance.

Date Output Methods

Method | Explanation
--- | ---
toString() | toString($format = null, $locale = null) Invoke directly or via the magic method __toString(). The toString() method automatically formats the date object's value according to the conventions of the object's locale, or an optionally specified `$locale`. For a list of supported format codes, see Self-Defined OUTPUT Formats with ISO.
toArray() | toArray() Returns an array representation of the selected date according to the conventions of the object's locale. The returned array is equivalent to PHP's getdate() function and includes: Number of day as 'day' (`Zend_Date::DAY_SHORT`) Number of month as 'month' (`Zend_Date::MONTH_SHORT`) Year as 'year' (`Zend_Date::YEAR`) Hour as 'hour' (`Zend_Date::HOUR_SHORT`) Minute as 'minute' (`Zend_Date::MINUTE_SHORT`) Second as 'second' (`Zend_Date::SECOND_SHORT`) Abbreviated timezone as 'timezone' (`Zend_Date::TIMEZONE`) Unix timestamp as 'timestamp' (`Zend_Date::TIMESTAMP`) Number of weekday as 'weekday' (`Zend_Date::WEEKDAY_DIGIT`) Day of year as 'dayofyear' (`Zend_Date::DAY_OF_YEAR`) Week as 'week' (`Zend_Date::WEEK`) Delay of timezone to GMT as 'gmtsecs' (`Zend_Date::GMT_SECS`)
toValue() | toValue($part = null) Returns an integer representation of the selected date `$part` according to the conventions of the object's locale. Returns `FALSE` when `$part` selects a non-numeric value, such as `Zend_Date::MONTH_NAME_SHORT`. Limitation of toValue() This method calls get() and casts the result to a PHP integer, which will give unpredictable results, if get() returns a numeric string containing a number too large for a PHP integer on your system. Use get() instead.
get() | get($part = null, $locale = null) This method returns the `$part` of object's date localized to `$locale` as a formatted string or integer. See get() for more information.
now() | now($locale = null) This convenience function is equivalent to `new Zend_Date()`. It returns the current date as a Zend_Date object, having `$locale`

## Working with Fractions of Seconds

Several methods support retrieving values related to a Zend_Date instance.

Date Output Methods

Method | Explanation
--- | ---
getFractionalPrecision() | Return the precision of the part seconds
setFractionalPrecision() | Set the precision of the part seconds

## Sunrise / Sunset

Three methods provide access to geographically localized information about the Sun, including the time of sunrise and sunset.

Miscellaneous Methods

Method | Explanation
--- | ---
getSunrise($location) | Return the date's time of sunrise
getSunset($location) | Return the date's time of sunset
getSunInfo($location) | Return an array with the date's sun dates