PHP forms are backed up after submission, and the contents of the form are emptied by default (when using Session_Start),
The workaround is to write the character output before the session_start ()
Copy Code code as follows:
Header ("Cache-control:private");
The caching of the Web page is controlled by the "Cache-control" in the HTTP message header, the common value has private, No-cache, Max-age, must-revalidate, etc., the default is private. Its role is divided into the following situations according to different ways of re browsing:
(1) Open a new window
Value is private, No-cache, and Must-revalidate, the server will be accessed again when a new window is opened.
If the Max-age value is specified, the server is not again accessed within the time of this value, for example:
Cache-control:max-age=5 (for 5 seconds after accessing this page will not go to the server)
(2) Enter in the Address bar
A value of private or must-revalidate accesses the server only for the first visit and is no longer accessible.
Value is No-cache, then it is accessed every time.
Value is Max-age, the access is not repeated until it expires.
(3) Press the Back button
Value is private, must-revalidate, and Max-age, it will not be accessed again.
Value is No-cache, the access is repeated each time
(4) Press the Refresh button
Regardless of the value, repeated access
When the Cache-control value is "No-cache", accessing this page does not leave a page backup on the Internet temporary article folder.
In addition, caching can also be affected by specifying a "Expires" value. For example, to specify that the Expires value is a long past time, if you repeatedly press ENTER in the Address bar when you visit the network, you will repeat the visit each time: Expires:fri, Dec 1999 16:00:00 GMT
For example: Prevent the page from being cached in IE
HTTP response message Header settings:
CacheControl = No-cache
Pragma=no-cache
Expires =-1
Expires is a good thing, if the Web page on the server often changes, set it to-1, indicating immediate expiration. If a page is updated daily 1 o'clock in the morning, you can set the expires to 1 o'clock in the morning the next day.
When the HTTP1.1 server specifies CacheControl = No-cache, the browser does not cache the Web page.
Legacy HTTP 1.0 Servers cannot use Cache-control headers.
So for backward compatibility with HTTP 1.0 servers, IE uses the Pragma:no-cache header to provide special support for HTTP.
If the client communicates with the server over a secure connection (https://) and the server returns Pragma:no-cache headers in the response,
Then Internet Explorer does not cache this response. Note: Pragma:no-cache only prevents caching when used in a secure connection, and if used in an unsecured page, the processing is the same as expires:-1, and the page is cached but marked as immediately expired.
Cache-control Message Header Field description
CACHE-CONTROL Specifies the caching mechanism that the request and response follow. Set in the request message or in the response message
Cache-control does not modify the caching process during another message processing process. The cached instructions at request include No-cache, No-store, Max-age, Max-stale, Min-fresh, only-if-cached, and the instructions in the response message include public, private, No-cache, No-store, No-transform, Must-revalidate, Proxy-revalidate, Max-age. The instructions in each message have the following meanings:
Public indicates that the response can be cached by any buffer.
Private indicates that the entire or partial response message for a single user cannot be handled by the shared cache. This allows the server to simply describe a partial response message from the user, which is not valid for other users ' requests.
No-cache indicates that a request or response message cannot be cached
No-store is used to prevent important information from being inadvertently released. Sending in a request message will not use caching for both request and response messages.
Max-age indicates that the client can receive a response that is not longer than the specified time in seconds.
Min-fresh indicates that the client can receive response times that are less than the current time plus a specified time.
Max-stale indicates that the client can receive response messages that exceed the timeout period. If you specify a value for the Max-stale message, the client can receive a response message that exceeds the specified value for the timeout period.
