PHP isset() | Check if a Variable is Set

The PHP isset() function is used when we need to check whether a variable is set or not. For example:

<?php
   if(isset($x))
   {
      echo "Variable \$x is set";
   }
   else
   {
      echo "Variable \$x is not set";
   }
?>

Since the variable $x is not set, therefore the output of above example is:

PHP isset() Syntax

The syntax of isset() function in PHP, is:

isset(variableOne, variableTwo, variableThree, ..., variableN);

At least one variable is required. Returns 1 if all given variables exists and are not NULL. Otherwise returns false or nothing. For example:

<?php
   $x = 10;
   $y = 20;
   $z = 30;
   
   echo "1: ", isset($x), "<BR>";
   echo "2: ", isset($x, $y), "<BR>";
   echo "3: ", isset($x, $y, $z), "<BR>";
   echo "4: ", isset($a), "<BR>";
   echo "5: ", isset($x, $a), "<BR>";
   echo "6: ", isset($x, $y, $s), "<BR>";
?>

The output of this PHP example on isset() function is shown in the snapshot given below:

In above example, the returned value 1 by isset() function, can also be considered as true.

PHP isset() Example

<?php
   $a = 10;
   $b = 0;
   $c = "jobails.com";
   $d = "PHP is Fun!";
   $e = 12.42;
   $f = true;
   $g = null;
   
   if(isset($a))
      echo "<p>The variable \$a is set, with $a</p>";
   if(isset($b))
      echo "<p>The variable \$b is set, with $b</p>";
   if(isset($c))
      echo "<p>The variable \$c is set, with $c</p>";
   if(isset($d))
      echo "<p>The variable \$d is set, with $d</p>";
   if(isset($e))
      echo "<p>The variable \$e is set, with $e</p>";
   if(isset($f))
      echo "<p>The variable \$f is set, with $f</p>";
   if(isset($g))
      echo "<p>The variable \$g is set, with $g</p>";
   if(isset($z))
      echo "<p>The variable \$z is set, with $z</p>";
   if(isset($myvar))
      echo "<p>The variable \$myvar is set, with $myvar</p>";
?>

The output should be:

The variable $a is set, with 10

The variable $b is set, with 0

The variable $c is set, with jobails.com

The variable $d is set, with PHP is Fun!

The variable $e is set, with 12.42

The variable $f is set, with 1

You can also print the counterpart, that is, the message when a variable is not set or defined, in this way:

<?php
   if(isset($myvar))
      echo "<p>The variable \$myvar is set, with $myvar</p>";
   else
      echo "<p>The variable \$myvar is not set</p>";
?>

Or directly using:

<?php
   if(!isset($myvar))
      echo "<p>The variable \$myvar is not set</p>";
?>

Since, in both the above example, the variable $myvar is not set, therefore the output of these two codes should be:

The variable $myvar is not set

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