I believe that as novices, we will have this doubt every time we use empty() and isset(): What is the difference between the two? When do you need to use empty()? When to use isset()? Today I will tell you about the difference between the two and their application scenarios.
1. Summary of differences:
Difference 1: empty() is a function, it has all the attributes of a function, has a return value, can use the function return value as a parameter, can use dynamic variable access, etc.;
isset() is Statement, which is an inherent logical structure of PHP, such as foreach, for, continue, etc., cannot be accessed using dynamic variables, and cannot use function return values as parameters; examples are as follows:
$a = 'empty'; $a('err');//TRUE empty(intval('1fa'));//FALSE;
Difference 2: When $a is defined, Regardless of whether its value is 0, false, null, '' and other empty values, the return value of empty() is true; the return value of isset() is also TRUE, isset will only return false when verifying undefined variables. ;
For example:
$a = 0;//'0',false,null,'','0.0'等空值 empty($a);//true empty('aaa');//false empty($b);//true isset($a);//true isset($b);//false,$b未定义
2. Application scenario:
a. When judging whether a variable is defined, isset() can be used;
Application: use the value of isset($_POST['submit']) when submitting the form to determine whether to submit the form.
b. When judging whether a variable is empty (you don’t need to know whether it is assigned a value), you can use empty();
Application: When performing form verification, you need to verify whether the value of the required item is empty.
c. When judging that a variable already exists and is not empty, you can use isset() first, and then empty();
Application: When uploading files, you need to judge that $_FILES has been assigned a value and is not empty.
The above has introduced the difference between empty and isset, including the relevant aspects. I hope it will be helpful to friends who are interested in PHP tutorials.

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SessionID is a mechanism used in web applications to track user session status. 1. It is a randomly generated string used to maintain user's identity information during multiple interactions between the user and the server. 2. The server generates and sends it to the client through cookies or URL parameters to help identify and associate these requests in multiple requests of the user. 3. Generation usually uses random algorithms to ensure uniqueness and unpredictability. 4. In actual development, in-memory databases such as Redis can be used to store session data to improve performance and security.

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