What is the difference between Cookie and Session in PHP7.0?

When developing Web applications, it is difficult to avoid using Cookies and Sessions. These two concepts play a vital role in many Web applications. In PHP7.0, Cookie and Session are two very common technologies, both of which are used to store and transfer data in web applications. Although they can both be used to store data, there are big differences between them. Let's take a closer look at the difference between Cookie and Session in PHP7.0.

1. Cookie

Cookie is a kind of data stored on the client and passed between the Web server and the client. Cookies usually contain some key information, such as user ID, user name, password, session ID, etc., and can be set, modified and read through the browser. The life cycle of a cookie can be persistent or temporary. If it is a persistent cookie, it can exist on the client until the expiration time, while a temporary cookie can only be used in the current session.

Cookie advantages:

1. Easy to use: You can use the PHP built-in function setcookie() to easily create and read cookies.
2. High security: Cookie information is stored on the client, and encryption and decryption are also performed on the client, making it difficult to be attacked by a man-in-the-middle.
3. Cross-domain support: Using cookies can easily transfer information between different domains.

Cookie Disadvantages:

1. There is a security risk: if the Cookie information is leaked, the attacker can obtain other information through the Cookie information, thereby attacking the website.
2. Very browser dependent: Many users choose to disable cookies, so availability cannot be 100% guaranteed.
3. Limited data size: The size of Cookie is limited to about 4KB, so it cannot store a large amount of data.

2. Session

Session is a kind of data stored on the Web server. It is similar to Cookie, but it is also very different. Using Session, the Web server assigns a unique ID (session ID) to each client to identify the client. When the client accesses the server, the server goes back to find the data corresponding to the client's session ID and reads it. and modifications. The life cycle of Session is usually shorter than that of Cookie. When the browser is closed, Session will expire, while Cookie can continue to exist after the browser is closed.

Session advantages:

1. High security: Session data is stored in the server, which can better protect sensitive data and avoid the risk of leakage.
2. Unlimited data volume: Since the data is stored in the server, it is not limited by the size of the browser cookie.
3. Can pass data across pages: Session can be used in all pages within the same domain.

Session Disadvantages:

1. It is stored on the server and takes up a lot of server resources.
2. Insufficient flexibility: Session is only suitable for situations where data needs to be transferred across pages and cannot be used for cross-domain transmission.
3. Users need to enable Cookie: When using Session, the user must enable the browser's Cookie function, otherwise Session cannot be used.

Use scenarios of Session and Cookie:

1. For some important data, such as user name, password, etc., it is best to use Session to store it.
2. Cookies can be used for less important data that needs to be transferred between different domains, such as user access records, shopping cart product lists, etc.
3. For some scenarios that require temporary storage of some data, such as verification codes, etc., cookies can also be used to store it.

In this article, we start with the definitions, advantages and disadvantages of Cookie and Session, and deeply explore their usage scenarios and their differences in PHP7.0. Although Cookies and Sessions have many differences, they are both integral parts of web applications. Only by choosing the appropriate way to process data according to actual needs can you better realize the functions of web applications.

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