Solution to the problem of missing content after form submission error (PHP website)_php skills

What should I do if the returned content disappears after a form submission error? Today we will analyze and solve this problem.

Condition overview:

A problem encountered when filling in form information and submitting it is that after the user fills in and submits the form, the program determines that it does not meet the requirements and returns. After returning, the previously filled form information will be cleared. It doesn't matter if the amount of information filled in is small, but if the amount of information filled in is relatively large, it will directly affect the good mood of the person filling in the information. Therefore, solving the problem of the filled-in content disappearing after a form submission error returns is an urgent issue to improve user experience.
For this kind of problem, we have summarized the following situations:
(1) The page uses the session_start function. One feature of this function is that it will force the current page not to be refreshed. The solution is to add the following code after this function:

header("Cache-control:private");//注意在本行之前你的PHP程序不能有任何输出 

There are several other solutions by adding
before session_start

session_cache_limiter('nocache'); //清空表单 
session_cache_limiter('private'); //不清空表单，只在session生效期间 
session_cache_limiter('public'); //不清空表单，如同没使用session一般 

The above setting of session will cause the seesion to be cached, which will cause the session information to be unable to be updated when you apply it to the session. For this reason, this article proposes several other solutions below.
(2) Use the Header method to set the message header Cache-control and add the following code to the page:
header('Cache-control: private, must-revalidate'); //Supports page bounce, please note that there cannot be any output before this line
(3) Use the session_cache_limiter method and add the following code to the page:
session_cache_limiter('private, must-revalidate'); //Note to write before the session_start method
The following is a supplementary explanation of the Cache-Control message header field:
Cache-Control specifies the caching mechanism that requests and responses follow. Setting Cache-Control in a request message or response message does not modify the caching process during the processing of another message. Cache directives during request include no-cache, no-store, max-age, max-stale, min-fresh, only-if- cached, directives in the response message include public, private, no- cache, no-store, no-transform, must-revalidate, proxy-revalidate, max-age. The meaning of the instructions in each message is as follows:

Public: indicates that the response can be cached by any cache.

Private: Indicates that all or part of the response message for a single user cannot be processed by the shared cache. This allows the server to only describe a partial response from a user that is not valid for other users' requests.

no-cache: Indicates that the request or response message cannot be cached

no-store: Used to prevent important information from being released unintentionally. Sending it in the request message will cause both the request and response messages to use caching.

max-age: Indicates that the client can receive responses with a lifetime no greater than the specified time in seconds.

min-fresh: Indicates that the client can receive responses with a response time less than the current time plus the specified time.

max-stale: Indicates that the client can receive response messages beyond the timeout period. If you specify a value for max-stale messages, the client can receive response messages that exceed the specified value of the timeout period.

After reading this article, if you encounter similar problems, you can completely solve them. Please remember that this solution is only for PHP websites.