Section 11.2. Date and Time Functions

11.2. Date and Time Functions PHP uses the standard Unix-style timestamp to work with dates. This is simply the number of seconds since January 1, 1970. You get the current timestamp using the time function, shown in Example 11-15. Example 11-15. A simple echo of the timestamp <?php $timestamp= time(); echo $timestamp; ?> This results in Figure 11-13. Figure 11-13. A Unix timestamp 1134511981 This is not exactly the most meaningful representation of the date and time. So instead, you can use the date function to translate the timestamp into a meaningful string. The date function takes a timestamp and a format string, as shown in Example 11-16. Example 11-16. Making the date and time appear like we expect <?php $timestamp= time(); echo date("m/d/y G.i:s",$timestamp); ?> This code returns the screen shown in Figure 11-14. Figure 11-14. An easy-to-read date and time from the date function Dates and times can be displayed in a variety of formats; these will be discussed next. 11.2.1. Display Formats Date and times are displayed in a variety of formats. In Example 11-16, we used a date format string of m/d/y G.i:s. Table 11-2 shows other possible components for those formats. Table 11-2. Time-formatting values Format Meaning Example value a am or pm Am A AM or PM AM d Day of the month 01 D Day or the week Sun F Month name January h Hours in 12-hour format with leading zeros 04 H Hours in 24-hour format with leading zeros 16 g Hours in 12-hour format without leading zeros 4 G Hours in 24-hour format without leading zeros 16 i Minutes 35 j Day of the month 2 l Day of the week as a name Sunday L Leap year (1 for yes, 0 for no) 1 m Month of the year abbreviated to three characters Jul M Month of the year July N Month of the year as number without leading zeros 7 s Seconds of the hour 58 S Suffix for the day th, nd, st, rd R Standardized date format Thu, 15 Dec 2005 16:49:39-0600 U Timestamp 1134512479 y Two-digit year 25 Y Four-digit year 2025 z Day of year 234 Z GMT offset in seconds (Greenwich Mean Time) -21600 (-6*60*60) 11.2.2. Arithmetic Adding or subtracting days and hours can be done by adding or subtracting seconds. While this may sound odd, it's not hard. To add two days to a timestamp, add 2*24*60*60 (2 days*24 hours*60 minutes*60 seconds) to the timestamp, as shown in Example 11-17. Example 11-17. Adding two days to the date <?php $timestamp= time(); echo date("m/d/y G.i:s",$timestamp); $seconds=2*24*60*60; $timestamp+=$seconds; echo "<br>new dates is:"; echo date("m/d/y G.i:s",$timestamp); ?> This outputs: 12/13/05 16.28:32 new dates is:12/15/05 16.28:32 Let's see what else you need to create dates with validation. 11.2.3. Validating Dates When you receive a user-supplied date, it's good practice, as with any other user-supplied data, to check that it's valid. You can use the checkdate function, shown in Example 11-18, to validate a date. It takes three parametersthe month, day, and yearfor a date to validate. If the date is valid, it returns trUE; otherwise, it returns FALSE. Example 11-18. Validating two dates <?php echo("Validating: 4/31/2005<br>"); if (checkdate(4,31,2005)) { echo('Date accepted.'); } else { echo ('Invalid date.'); } echo("<br>"); echo("Validating: 5/31/2005<br>"); if (checkdate(5,31,2005)) { echo('Date accepted.'); } else { echo ('Invalid date.'); } ?> As you can tell by our example in Figure 11-15, the 31 April 2005 date was invalid, yet 31 May 2005 was valid. This can happen because of a typo or a user just entering wrong information. Figure 11-15. Only some months have 31 days Once you know that you have the valid segments of a date, you can create a timestamp. 11.2.4. Using mktime to Create a Timestamp It's fairly easy to get the current time and date using date, but if you're trying to create a date and all you have are the components of the date such as month, day, and year, you'll need to use the mktime function. The mktime function takes these parameters: Hour Minute Second Month Day of the month Year You can omit some of the parameters when calling mktime, and they'll be filled in from the current time. mktime is a timestamp, which is an integer containing the number of seconds between the Unix Epoch of January 1 1970 00:00:00 GMT and the time specified. You can't omit them out of order though. Example 11-19 checks whether the date is valid, and then creates a timestamp. Example 11-19. Creating a timestamp from the components of a date <?php echo("Validating: 5/31/2005<br>"); if (checkdate(5,31,2005)) { echo('Date accepted: '); $new_date=mktime(18,05,35,5,31,2005); echo date("r",$new_date); } else { echo ('Invalid date.'); } echo("<br>"); ?> When run, this code produces the screen shown in Figure 11-16. Figure 11-16. A timestamp created from its components Now that we've covered dates and times, it's time to head onto more exciting topics. Note that the number of the year might be a two- or four-digit value, between 0 to 69 mapping to 2000 to 2069 and 70 to 100 to 1970 to 2000. On systems where time_t is a 32-bit signed integer, which is most common today, the valid range for the year is somewhere between 1901 and 2038. This limitation is fixed since the release of PHP 5.1.0.