isset vs empty vs is_null

Last modified on February 24th, 2017 by Vincy.

PHP has multiple functions used to check PHP variables with respect to their initialized values. These functions are,

isset() is to check if a variable is set with a value.
empty() is to check if a given variable is empty. The difference with isset() is, isset has NULL check enabled.
is_null() – It is to check whether a variable is defined as NULL.

Ok! Now find the difference!

I feel the effective way to communicate the difference would be with the help of a TRUTH TABLE,

	“”	“apple”	NULL	FALSE	0	undefined
*empty()*	TRUE	FALSE	TRUE	TRUE	TRUE	TRUE
*is_null()*	FALSE	FALSE	TRUE	FALSE	FALSE	ERROR
*isset()*	TRUE	TRUE	FALSE	TRUE	TRUE	FALSE

Code to Understand the Difference

<?php

print "<br/>ISSET: <br/>";
$var = "";
print "isset():". isset($var)."<br/>";
$var = "apple";
print "isset('apple'):". isset($var)."<br/>";
$var = NULL;
print "isset('NULL'):". isset($var)."<br/>";
$var = FALSE;
print "isset('FALSE'):". isset($var)."<br/>";
$var = 0;
print "isset('0'):". isset($var)."<br/>";
print "isset(undefined):". isset($var3)."<br/>";

print "<br/>EMPTY: <br/>";
$var = "";
print "empty():". empty($var)."<br/>";
$var = "apple";
print "empty('apple'):". empty($var)."<br/>";
$var = NULL;
print "empty('NULL'):". empty($var)."<br/>";
$var = FALSE;
print "empty('FALSE'):". empty($var)."<br/>";
$var = 0;
print "empty('0'):". empty($var)."<br/>";
print "empty(undefined):". empty($var1)."<br/>";

print "<br/>IS_NULL: <br/>";
$var = "";
print "is_null():". is_null($var)."<br/>";
$var = "apple";
print "is_null('apple'):". is_null($var)."<br/>";
$var = NULL;
print "is_null('NULL'):". is_null($var)."<br/>";
$var = FALSE;
print "is_null('FALSE'):". is_null($var)."<br/>";
$var = 0;
print "is_null('0'):". is_null($var)."<br/>";
print "is_null(undefined):". is_null($var2)."<br/>";

?>

Output:

ISSET: isset():1 isset(‘apple’):1 isset(‘NULL’): isset(‘FALSE’):1 isset(‘0’):1 isset(undefined): EMPTY: empty():1 empty(‘apple’): empty(‘NULL’):1 empty(‘FALSE’):1 empty(‘0’):1 empty(undefined):1 IS_NULL: is_null(): is_null(‘apple’): is_null(‘NULL’):1 is_null(‘FALSE’): is_null(‘0’): Notice: Undefined variable: var2 in C:\xampp\htdocs\phppot_samples\php_isset\php_isset.php on line 40 is_null(undefined):1

This PHP code tutorial was published on October 4, 2013.

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