PHP uses header to set browser cache

The function of the header() function is to send a raw HTTP header [Http Header] to the client.
The header is a string sent by the server before transmitting HTML data to the browser using the HTTP protocol. A blank line is required between the header
and the HTML file. Now let me share with you a PHP technology that uses headers to set browser cache.

<?php     
//定义一个合理缓存时间。合理值屈居于页面本身、访问者的数量和页面的更新频率，此处为3600秒(1小时)。     
$cache_time = 60 * 60;    
$modified_time = @$_SERVER[&#39;HTTP_IF_MODIFIED_SINCE&#39;];    
if( strtotime($modified_time)+$cache_time > time() ){     
    header("HTTP/1.1 304");     
    exit;     
}     
//发送Last-Modified头标，设置文档的最后的更新日期。     
header ("Last-Modified: " .gmdate("D, d M Y H:i:s", time() )." GMT");     
     
//发送Expires头标，设置当前缓存的文档过期时间，GMT格式，我们使用的是GMT+8时区    
header ("Expires: " .gmdate("D, d M Y H:i:s", time()+$cache_time )." GMT");     
     
//发送Cache_Control头标，设置xx秒以后文档过时,可以代替Expires，如果同时出现，max-age优先。     
header ("Cache-Control: max-age=$cache_time");     
echo time();     
?>

About using the header() function. I still have a lot of knowledge points for you. Next, the editor will continue to share with you the usage of the PHP header function and its precautions.

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