The difference between empty and isset

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.