Web Database Applications with PHP and MySQL, 2nd Edition

Dates and Times

There are several PHP library functions that work with dates and times. Most either generate a Unix timestamp or format a Unix timestamp in a human-readable form. Validation using dates, and working with the flexible PEAR Date package, is discussed in Chapter 9. In this section, we introduce timestamps and PHP library functions that work with Dates and Times.

Generating a Timestamp

A Unix timestamp consists of the number of seconds since the arbitrarily chosen time 1 January 1970 00:00:00 Greenwich Mean Time. Most systems represent a timestamp using a signed 32-bit integer, allowing a range of dates from December 13, 1901 through January 19, 2038. While timestamps are convenient to work with, care must be taken when manipulating timestamps to avoid integer overflow errors. While PHP automatically converts integers that overflow to floats, these values aren't valid timestamps.

Warning

In the Microsoft Windows environment, the timestamp functions don't support negative timestamps and can be used only with dates between January 1, 1970 and January 19, 2038.

Current time

PHP provides several functions that generate a Unix timestamp. The simplest:

integer time( )

returns the timestamp for the current date and time, as shown in this fragment:

// prints the current timestamp: e.g., 1064699133
print time( );

Creating timestamps with mktime( ) and gmmktime( )

To create a timestamp for a past or future date in the range December 13, 1901 through January 19, 2038, the mktime( ) and ...