Pragma:no-cache

PHP Advanced and object-oriented Programminglarry Ullman last-modified Last modified time expires expiration pragma compile hint Cache-control Cache control such as the cache system discovers that the value of last-modified is closer to the current time than the page cache version, it knows that the updated page version from the server should be used.

Caching-both in Web browsers and proxy Servers-can is affected using PHP ' s header () function. Four header types is involved:

last-modified

expires

pragma

Cache-control

The first three header types is part of the HTTP 1.0 standard. The last-modified header uses a UTC (coordinated Universal time) date-time value. If a caching system sees that the last-modified Valueis more recent than the date on the cached version of the page, it kn oWS to use the new version from the server. Expires is used as a indicator as to when a cached version of the page should no longer be used (Ingreenwich Mean time).

Setting an Expires value in the past should all force the page from theserver to be used:

Header ("Expires:mon, Jul 1997 05:00:00 GMT");

Pragma is just a declaration for how the page data should be handled. To avoid caching of a page, use

Header ("Pragma:no-cache")

The Cache-control headers were added in HTTP 1.1 and are a more finely tuned option.

Directive meaning

Public Can be cached anywhere

Private only cached by browsers

No-cache cannot be cached anywhere

Must-revalidate Caches must check for newer versions

Proxy-revalidate Proxy caches must check for newer versions

Max-age A duration, in seconds, then the content is cacheable

S-maxage Overrides The Max-age value for shared caches

Keep all systems from caching a page

Header ("Last-modified:mon, 05:00:00 GMT"); Right now!

Header ("Expires:mon, Jul 1997 05:00:00 GMT"); The Back then!

Header ("Pragma:no-cache");

Header ("Cache-control:no-cache");

Pragma:no-cache