What does isset() function?

by

The isset() function checks if the variable is defined and not null.

In PHP, the isset() function is used to determine whether a variable is set and is not NULL. It returns true if the variable exists and has a value other than NULL. Otherwise, it returns false.

Here’s a simple explanation:

php
$var = "Hello";

// isset() returns true because $var is set and has a value
if (isset($var)) {
echo '$var is set.';
} else {
echo '$var is not set.';
}

// Unset the variable
unset($var);

// isset() returns false because $var is unset
if (isset($var)) {
echo '$var is set.';
} else {
echo '$var is not set.';
}

Output:

csharp
$var is set.
$var is not set.

In an interview setting, you could explain the purpose and usage of isset(), along with providing examples like the one above to illustrate its behavior.