PHP | isset() Function

The isset() function is an inbuilt function in PHP which is used to determine if the variable is declared and its value is not equal to NULL.

Syntax:

bool isset( mixed $var [, mixed $... ] )

Parameters: This function accept one or more parameter as mentioned above and described below:

• $var: It contains the variable which need to check.
• $…: It contains the list of other variables.

Return Value: It returns TRUE if var exists and its value not equal to NULL and FALSE otherwise.

Below examples illustrate the isset() function in PHP:

Example 1:

<?php

$str = "GeeksforGeeks";

// Check value of variable is set or not
if(isset($str)) {
    echo "Value of variable is set";
}
else {
    echo "Value of variable is not set";
}

$arr = array();

// Check value of variable is set or not
if( !isset($arr[0]) ) {
    echo "\nArray is Empty";
}
else {
    echo "\nArray is not empty";
}

?>

Output:

Value of variable is set
Array is Empty

Output:

Example 2:

<?php

$num = 21;
var_dump(isset($num));

$arr = array(
        "a" => "Welcome",
        "b" => "to",
        "c" => "GeeksforGeeks"
    );

var_dump(isset($arr["a"]));
var_dump(isset($arr["b"]));
var_dump(isset($arr["c"]));
var_dump(isset($arr["Geeks"]));

?>

Output:

bool(true)
bool(true)
bool(true)
bool(true)
bool(false)

Reference: https://www.php.net/manual/en/function.isset.php