What does isset in php do?

In PHP, isset() is a function that checks whether a variable is set and not NULL. Returns true if the variable exists and is not NULL, false otherwise.

In PHP, isset() is a function that checks if a variable is set and not NULL. Returns true if the variable exists and is not NULL, false otherwise.

This function is particularly useful when dealing with form data, array elements, or object properties, because it can help you determine whether these values ​​exist and are not NULL.

Example:

php

$name = '';  
  
if (isset($name)) {  
    echo "变量已设置";  
} else {  
    echo "变量未设置";  
}

In this example, because $name is already set and is an empty string, isset($name) will return true, and Output "Variable is set".

It should be noted that isset() only checks whether the variable has been set and is not NULL. It does not check the type or value of the variable. If you need more complex checks, you may need to use other functions or logic.

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