The difference between cookie and session in php

Get to know cookies

Cookie in English means cookies and small desserts. In web applications, it is also similar to program feasts. A little dessert, in the Internet, Cookie actually refers to a small amount of information, which is created by the Web server and stores the information in the file on the user's computer. Its main function is to record the basic information of the user in the web application, which can also be called browsing. server cache or cookies. (Recommended learning: PHP video tutorial)

Web applications are based on the http protocol for network interaction, and the http protocol does not record the information submitted by each web page, and many websites All have membership functions. If you have to resubmit your membership information every time you jump to a page, the task will be too cumbersome, so Cookie was born.

The web application can generate a cookie information from the server-side code and save it in the client's browser during operation, generating a very small file. At this time, the file is stored in the RAM running memory. If the user closes The browser will automatically delete the cookie information; if the program generates a cookie with a time setting, the cookie file will be stored in the physical memory. The next time you visit the same web application, the web application can still obtain it within the set time range. cookie information.

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Understanding session

Session concept: In computers, especially in network applications, it is called "session control". The Session object stores the properties and configuration information required for a specific user session.

In this way, when the user jumps between the application's Web pages, the variables stored in the Session object will not be lost, but will persist throughout the user session. When a user requests a Web page from an application, the Web server automatically creates a Session object if the user does not already have a session.

When the session expires or is abandoned, the server will terminate the session. One of the most common uses of Session objects is to store user preferences. For example, if the user indicates that he or she does not like to view graphics, this information can be stored in the Session object.

Session mechanism: Session content is generally stored in the server in the form of files, and the local browser will store a cookie value corresponding to the session file in the server. The cookie stores the key value "PHPSESSID "Seeion_id value.

When a user accesses a web application, every time an http request occurs during a jump, the cookie value that stores session_id will be automatically sent to it. Therefore, all pages of the web application can obtain this SESSION_ID value, that is, The session value stored in the server can be obtained through session_id. When the user closes the browser, the session_id stored in the cookie is automatically cleared. Generally, the session files stored by the server will also be automatically cleared after 30 minutes.

The difference between COOKIE and SESSION

(1)Storage location:Cookie is stored in the client browser, which is relatively unsafe; Session content The file is stored in the server, usually in the tmp folder in the root directory, which is relatively safer.

(2)Quantity and size limit: The data stored by Cookie will have different restrictions in different browsers. Generally, under the same domain name, the number of Cookie variables is controlled within 20 , the size of each cookie value is controlled within 4kb. There is no limit on the size or number of session values, but if there are too many, it will increase the pressure on the server.

(3)Content difference: The content saved by the cookie is a string, while the data saved by the session in the server is an object.

(4)Path difference: session cannot distinguish paths. During the same user's visit to a website, all sessions can be accessed anywhere; and if the cookie is set Path parameters, then cookies under different paths on the same website cannot access each other.

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