Zend_Date | Zend_Date Programmer's Reference Guide | Theory of Operation

# Introduction

The Zend_Date component offers a detailed, but simple API for manipulating dates and times. Its methods accept a wide variety of types of information, including date parts, in numerous combinations yielding many features and possibilities above and beyond the existing PHP date related functions. For the very latest manual updates, please see » our online manual (frequently synced to Subversion).

Although simplicity remains the goal, working with localized dates and times while modifying, combining, and comparing parts involves some unavoidable complexity. Dates, as well as times, are often written differently in different locales. For example, some place the month first, while other write the year first when expressing calendar dates. For more information about handling localization and normalization, please refer to Zend_Locale.

Zend_Date also supports abbreviated names of months in many languages. Zend_Locale facilitates the normalization of localized month and weekday names to timestamps, which may, in turn, be shown localized to other regions.

# Always Set a Default Timezone

Before using any date related functions in PHP or Zend Framework, first make certain your application has a correct default timezone, by either setting the TZ environment variable, using the date.timezone php.ini setting, or using » date_default_timezone_set(). In PHP, we can adjust all date and time related functions to work for a particular user by setting a default timezone according to the user's expectations. For a complete list of timezone settings, see the » CLDR Timezone Identifier List.

Example #1 Setting a Default Timezone

1. // timezone for an American in California
2. date_default_timezone_set('America/Los_Angeles');
3. // timezone for a German in Germany
4. date_default_timezone_set('Europe/Berlin');

When creating Zend_Date instances, their timezone will automatically become the current default timezone! Thus, the timezone setting will account for any Daylight Savings Time (DST) in effect, eliminating the need to explicitly specify DST.

Keep in mind that the timezones UTC and GMT do not include Daylight Saving Time. This means that even if you define per hand that Zend_Date should work with DST, it would automatically be switched back for the instances of Zend_Date which have been set to UTC or GMT.

# Why Use Zend_Date?

Zend_Date offers the following features, which extend the scope of PHP date functions:

- Simple API

  Zend_Date offers a very simple API, which combines the best of date and time functionality from four programming languages. It is possible, for example, to add or compare two times within a single row.

- Completely internationalized

  All full and abbreviated names of months and weekdays are supported for more than 130 languages. Methods support both input and the output of dates using the localized names of months and weekdays, in the conventional format associated with each locale.

- Unlimited timestamps

  Although PHP 5.2 docs state, "The valid range of a timestamp is typically from Fri, 13 Dec 1901 20:45:54 GMT to Tue, 19 Jan 2038 03:14:07 GMT," Zend_Date supports a nearly unlimited range, with the help of the BCMath extension. If BCMath is not available, then Zend_Date will have reduced support only for timestamps within the range of the float type supported by your server. "The size of a float is platform-dependent, although a maximum of ~1.8e308 with a precision of roughly 14 decimal digits is a common value (that's 64 bit IEEE format)." [ » http://www.php.net/float ]. Additionally, inherent limitations of float data types, and rounding error of float numbers may introduce errors into calculations. To avoid these problems, Zend Framework's I18n components use BCMath extension, if available.

- Support for ISO-8601 date specifications

  ISO-8601 date specifications are supported. Even partially compliant ISO-8601 date specifications will be identified. These date formats are particularly useful when working with databases. for example, even though MsSQL and » MySQL differ a little from each other, both are supported by Zend_Date using the Zend_Date::ISO_8601 format specification constant. When date strings conform to "Y/m/d" or "Y-m-d H:i:s", according to PHP date() format tokens, use Zend_Date's built-in support for ISO-8601 formatted dates.

- Calculate sunrise and sunset

  For any place and day, the times for sunrise and sunset can be displayed, so that you won't miss a single daylight second for working on your favorite PHP project :)

Zend_Date | Zend_Date Programmer's Reference Guide | Theory of Operation