PHP isset() Function

The isset() function in PHP checks whether a variable is declared and not NULL. It returns true if the variable exists and has a non-NULL value, and false otherwise, without modifying the variable.

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: In this example we checks if the $str variable is set using isset(). It also verifies if the first element of an empty array $arr is set, printing appropriate messages for both checks.

<?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";

    }

?>

Value of variable is set
Array is Empty

Example 2: In this example we use isset() to check if the variable $num and specific elements in the $arr array are set. It outputs true for existing elements and false for non-existent ones.

<?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"]));

?>

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