PHP using the header () function to set the browser cache code _php tips

This involves 4 kinds of header types:

Last-modified (last modification time);
Expires (valid term);
Pragma (compiling instructions);
Cache-control (cache control);
The first three headers belong to the HTTP1.0 standard. The header last-modified uses a UTC datetime value. If the cache system finds that the Last-modified value is more connected than the page cache version
In the near current time, he knew that a new version should be used from the server.

Expires indicates when the cached version should expire (Greenwich Mean Time). Setting it to a previous time will force the use of pages on the server.

pragma life. How the page data should be processed. You can avoid caching a page in this way:

Header ("Pragma:no-cache");

Cache-co0ntrol headers are added in HTTP1.1 to achieve finer control (and should continue to use HTTP1.0 headers). The Cache-control settings have
Many, as in the following table:

Instructions	Meaning
Public	Can be cached in any place
Private	Can only be cached by the browser
No-cache	cannot be cached anywhere
Must-revalidate	Cache must check for newer versions
Proxy-revalidate	Proxy cache must check for newer versions
Max-age	The period in which content can be cached, expressed in seconds
S-maxage	Overwrite max-age settings for shared cache

The following example uses the header () to set the browser's cache:

Copy Code code as follows:

<?php # Script 2.7-view_tasks.php
Connect to the database:
$DBC = @mysqli_connect (' localhost ', ' username ', ' password ', ' Test ') OR die (' <p>could not connect to the database!& Lt;/p></body>Get the latest dates as timestamps:
$q = ' SELECT unix_timestamp (max (date_added)), Unix_timestamp (Max (date_completed)) from tasks ';
$r = Mysqli_query ($dbc, $q);
List ($max _a, $max _c) = Mysqli_fetch_array ($r, mysqli_num);
Determine the greater timestamp:
$max = ($max _a > $max _c)? $max _a: $max _c;
Create a cache interval in seconds:
$interval = 60 * 60 * 6; 6 hours
Send the header:
Header ("last-modified:"). Gmdate (' R ', $max));
Header ("Expires:"). Gmdate ("R", ($max + $interval));
Header ("cache-control:max-age= $interval");
?>

1. When you connect to the database, get the latest date value date_added,date_completed in the datasheet, convert the return value to an integer with the Unix_timestamp () function, and then get the maximum value given to $max.
2. Define a reasonable cache time.

Copy Code code as follows:

$interval =60*60*6

Reasonable value of the page itself, the number of visitors and the update frequency of the page, the above code is 6 hours.
3. Send last-modified headers.

Copy Code code as follows:

Header ("Last-modified:" Gmdate ("R", ($max + $interval));

When the Gmdate () function uses the parameter "R", the corresponding date format is returned according to the HTTP specification.
4. Set the Expires header.

Copy Code code as follows:

Header ("Expires:"). Gmdate ("R", ($max + $interval));

5. Set the Cache_control header.

Copy Code code as follows:

Header ("cache-control:max-age= $interval");