How to start Session session in php

Session settings are different from Cookie and must be started first. Session_start()Function must be called in PHP so that the PHP core program can transfer the content related to Session. Build environment Variables are preloaded into memory.

Use the session_start() function to start the session. The syntax format is as follows:

session_start(void);   // 创建  Session，开始一个会话，进行 Session 初始化

session_start()This function has no parameters, and the return value is TURE. This function has two main purposes, it starts a session and it returns an existing session.

When you visit the website for the first time, the session_start() function will create a unique Session ID and automatically save this Session ID to the client cookie through the HTTP response header. . At the same time, the page creates a file named with this Session ID on the server side to save the user's session information.

When the same user visits this website again, the Session ID saved in the client's cookie will be automatically brought over through the HTTP request header. At this time, the session_start() function will Instead of allocating a new Session ID, it will look for a Session file with the same name as the Session ID on the server's hard disk, read out the session information previously saved for this user, and apply it in the current script to track this User purpose.

So during the session, the same user will use the same Session ID when accessing any page on the server.

Note: Usually, the session_start() function is called at the beginning of the page, and then the session variable is logged into the data $_SESSION.

Note: If you use a Cookie-based Session, there cannot be any output content before using this function to open the Session. Because when a Cookie-based Session is actually opened, the session_start() function is called to generate a unique Session ID, which needs to be saved in the cookie of the client computer, so the session_start() function is used Previously, the browser could not produce any output, not even spaces or blank lines, otherwise an error would be generated by outputting string.

If you don’t want to use the session_start() function to open the Session in every script, you can set session.auto_start = 1 in php.ini, no You need to call the session_start() function every time before using Session. But enabling this option also has some limitations, that is, objects cannot be put into Session because the class definition must be loaded before starting Session. Therefore, it is generally not recommended to use session.auto_start to open the Session.

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