Learning PHP, MySQL, and JavaScript

Date and Time Functions

To keep track of the date and time, PHP uses standard Unix timestamps, which are simply the number of seconds since the start of January 1, 1970. To determine the current timestamp, you can use the time function:

echo time();

Because the value is stored as seconds, to obtain the timestamp for this time next week, you would use the following, which adds 7 days × 24 hours × 60 minutes × 60 seconds to the returned value:

echo time() + 7 * 24 * 60 * 60;

If you wish to create a timestamp for a given date, you can use the mktime function. Its output is the timestamp 946684800 for the first second of the first minute of the first hour of the first day of the year 2000:

echo mktime(0, 0, 0, 1, 1, 2000);

The parameters to pass are, in order from left to right:

• The number of the hour (0–23)

• The number of the minute (0–59)

• The number of seconds (0–59)

• The number of the month (1–12)

• The number of the day (1–31)

• The year (1970–2038, or 1901–2038 with PHP 5.1.0+ on 32-bit signed systems)

Note

You may ask why you are limited to the years 1970 through 2038. Well, it’s because the original developers of Unix chose the start of the year 1970 as the base date that no programmer should need to go before! Luckily, because as of version 5.1.0, PHP supports systems using a signed 32-bit integer for the timestamp, dates 1901 to 2038 are allowed on them. However, a problem even worse than the first comes about because the Unix designers also decided that nobody would be using Unix after about ...