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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

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