The concept of Session in PHP_PHP Tutorial

What is Session? It is difficult to directly translate Session into Chinese, and it is generally translated into time domain. In computer terminology, Session refers to the time interval between an end user communicating with an interactive system, usually referring to the time elapsed between registering to enter the system and logging out of the system. Specifically, Session in the Web refers to the time that elapses from entering the website to closing the browser when a user browses a website, which is also the time spent by the user browsing the website. Therefore, we can see from the above definition that Session is actually a specific time concept.
It should be noted that the concept of a Session needs to include a specific client, a specific server and uninterrupted operation time. The Session in which user A establishes a connection with server C and the Sessions in which user B establishes a connection with server C are two different Sessions.
So what is the solution for Session? We know that users often need to browse many web pages when visiting a website. For a website built with PHP, users need to execute many PHP scripts during their visit. However, due to the characteristics of the HTTP protocol itself, users need to re-establish a connection with the Web server every time they execute a PHP script. And due to the characteristics of stateless memory, this connection cannot obtain the status of the last connection. In this way, the user assigns a value to a variable in one PHP script, but cannot get the value of the variable in another PHP script. For example, the user sets $user="wind" in the PHP script responsible for logging in, but cannot obtain the value of "wind" by calling $user in another PHP script. That is, global variables cannot be set in PHP. The variables defined in each PHP script are local variables that are only valid within this script.
The Session solution is to provide a method to define global variables in PHP scripts, so that this global variable is valid for all PHP scripts in the same Session. As we mentioned above, Session is not a simple time concept. A Session also includes specific users and servers. Therefore, in more detail, the scope of global variables defined in a Session refers to all PHP accessed by the user corresponding to this Session.
For example, user A defines a global variable $user="wind" through Session, and user B defines a global variable $user="jane" through Session. Then in the PHP script accessed by user A, the value of $user is wind.

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