Difference between isset() and empty() Functions

The isset() and empty() functions in PHP are used for variable checking but serve different purposes. isset() checks if a variable is set and not null, while empty() checks if a variable is considered empty, like 0, false, null, or an empty string.

empty() Functions

The empty() function in PHP checks whether a variable is considered "empty." It returns true for values like 0, "0", false, NULL, empty arrays, empty strings, or if the variable is not set.

Syntax:

bool empty ( $var )

Parameter: This function accepts a single parameter as shown in above syntax and described below.

• $var: Variable to check whether it is empty or not.

Example: In this example we demonstrates the empty() function, which returns True for variables considered "empty" (e.g., 0, 0.0, "0", NULL, false, empty arrays, and undefined variables).

<?php

    // PHP code to demonstrate the working 
    // of empty() function
    $var1 = 0;
    $var2 = 0.0;
    $var3 = "0";
    $var4 = NULL;
    $var5 = false;
    $var6 = array();
    $var7 = "";

    // For value 0 as integer
    empty($var1) ? print_r("True\n") : print_r("False\n");

    // For value 0.0 as float
    empty($var2) ? print_r("True\n") : print_r("False\n");

    // For value 0 as string
    empty($var3) ? print_r("True\n") : print_r("False\n");

    // For value Null
    empty($var4) ? print_r("True\n") : print_r("False\n");

    // For value false
    empty($var5) ? print_r("True\n") : print_r("False\n");

    // For array
    empty($var6) ? print_r("True\n") : print_r("False\n");

    // For empty string
    empty($var7) ? print_r("True\n") : print_r("False\n");

    // For not declare $var8
    empty($var8) ? print_r("True\n") : print_r("False\n");

?>

True
True
True
True
True
True
True
True

isset() Function

The isset() function in PHP checks whether a variable is set and is not NULL. It returns true if the variable has a value other than NULL, and false if it's unset or NULL.

Syntax:

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

Parameters: This function accepts one or more parameters as mentioned above and described below.

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

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

Example : In this example we use isset() to check if a variable or array element is set. It confirms if $str is set and checks if the first element of $arr is defined.

<?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

PHP program using both isset() and empty() functions:

Example: In this example we demonstrates isset() and !empty() functions. It first checks if $num is set with isset(), then verifies if $num is not empty using the !empty() function.

<?php

// PHP function to demonstrate
// isset() and !empty() function

// initialize a variable
$num = '0';

// Check isset() function
if( isset ( $num ) ) {
    print_r( $num . " is set with isset function");
}

// Display new line
echo "\n";

// Initialize a variable
$num = 1;

// Check the !empty() function
if( !empty ( $num ) ) {
    print_r($num . " is set with !empty function");
}

?>

Output:

0 is set with isset function
1 is set with !empty function

Difference between isset() and empty() function: