Using Predefined Constants for Date Format

We can use Predefined Constants for Date format in date() instead of the conventional date format strings since PHP 5.1.0.

Predefined Date Format Constants Available

DATE_ATOM - Atom (2016-07-22T14:50:01+00:00)

DATE_COOKIE - HTTP Cookies (Friday, 22-Jul-16 14:50:01 UTC)

DATE_RSS - RSS (Fri, 22 Jul 2016 14:50:01 +0000)

DATE_W3C - World Wide Web Consortium (2016-07-22T14:50:01+00:00)

DATE_ISO8601 - ISO-8601 (2016-07-22T14:50:01+0000)

DATE_RFC822 - RFC 822 (Fri, 22 Jul 16 14:50:01 +0000)

DATE_RFC850 - RFC 850 (Friday, 22-Jul-16 14:50:01 UTC)

DATE_RFC1036 - RFC 1036 (Fri, 22 Jul 16 14:50:01 +0000)

DATE_RFC1123 - RFC 1123 (Fri, 22 Jul 2016 14:50:01 +0000)

DATE_RFC2822 - RFC 2822 (Fri, 22 Jul 2016 14:50:01 +0000)

DATE_RFC3339 - Same as DATE_ATOM (2016-07-22T14:50:01+00:00)

Usage Examples

echo date(DATE_RFC822);

This will output: Fri, 22 Jul 16 14:50:01 +0000

echo date(DATE_ATOM,mktime(0,0,0,8,15,1947));

This will output: 1947-08-15T00:00:00+05:30