PHP isset function statement tutorial and example script code

Check whether a variable is set with isset()

isset() returns true when a variable exists and its value is not null. It can also check nested array keys safely without producing an undefined-key warning.

<?php
$user = ['name' => 'Asha'];
if (isset($user['name'])) {
    echo $user['name'];
}
?>

<?php
$x="some value"; // assigned a string to the variable $x here
if(isset($x)){ // checking the existence of the variable by isset
echo "The variable exists";
}else{
 echo " Variable does not exists ";
}
?>

Output

The variable exists

Some time we have to check the existence of a variable before using it for our further processing. The return value will be either true or false.

The code above will test the existence of the variable $x and since we have already declared it at first line so the PHP IF condition will return true and the statement inside if condition will be evaluated.
Difference between isset() and empty()

Variable is Null

If the variable is set to Null then isset will return FALSE. Here is the code

<?php
$test_var=null;
if(isset($test_var)){echo " Output : True";}
else{
echo "Output : False ";
}?>

Output is

Output : False

Variable is empty

In the above code, Let us change the variable like this

$test_var='';

The output will change to

Output : True

Checking more than one variable

If we check more than one variable then we will get out True if all the variables are True.

<?php
$test_var1='';
$test_var2='';
unset($test_var2);
if(isset($test_var1,$test_var2)){echo " Output : True";}
else{
echo "Output : False ";
}
?>

By using unset() function we have removed one variable hence the output of isset function will be FALSE

empty() to check variable

This function is used in PHP LOGIN SCRIPT and PHP LOGIN LOGOUT script to check the existence of session variables.

Using isset to check array variable

<?php
$my_array=array("first"=>'test', "second"=>34, "third"=>'');

var_dump(isset($my_array['first'])); // bool(true)
var_dump(isset($my_array['second'])); // bool(true)
var_dump(isset($my_array['new_one'])); // bool(false)
?>

How to create PHP Array

Checking elements with NULL value

$input=array('One' =>1,'Two'=>null);
echo var_dump(isset($input['Two'])); // bool(false)

If the element is equal to NULL then output became False, however array_key_exists() returns True.

$input=array('One' =>1,'Two'=>null);

if(array_key_exists('Two',$input)){ // True 
echo "Key is available ";	// this is the output
}else{
echo "Key is NOT available ";	
}
echo "<br>";
//// 
echo var_dump(isset($input['Two'])); // bool(false)

Using isset() with session variable

if(isset($_SESSION['userid']) && !empty($_SESSION['userid'])) {
 echo " session  is available, Welcome $_SESSION[userid] ";
}else{
 echo " No Session , Please Login ";
exit;
}

isset(): Check the variable