PHP, Structures and Functions, Fundamental Syntaxes

This function returns a VOID value when it tests the following variable types:

STRING, NUMERIC, BOOLEAN, ARRAY, NULL, RESOURCE or OBJECT.

One way to visualize the test result is to use var_dump, however, it is better to use if as a conditional evaluation framework.

CAN NOT BE USED OVER CONSTANTS

Its BEHAVIOR may be AFFECTED,
in the case of VARIABLES TREATED BY FUNCTIONS.

Evaluation goes from left to right and stops as soon as an unset variable is encountered.

All variables destroyed by unset are set to NULL.

Because it is a simple language construction, it can not be considered a function.

Therefore, it can not be called using variable functions, which is why we use isset and !isset and not unset or !unset to verify its effectiveness.

It is possible to unset even object properties visible in current context.

Since PHP 5.0.0 it is not possible to unset variables inside an OBJECT.


<?php


void unset ( mix $var1, [mix var2, ..., mix $varN ] );


where,

$var1 = FIRST VARIABLE to destroy

$var2 = SECOND VARIABLE to destroy

. . . . . . . . . . . . . . .

$varN = LAST VARIABLE to destroy

?>

$var1

The first variable to destroy.

$var2 ... $varN

The rest of other variables to destroy.

EXERCISE


<?php

function UNsett01 ($var) 
{ 
if(!isset($var)) 
{ 
var_dump($var); 
echo '<br>THIS VARIABLE IS UNSET<br><br>'; 
} 
else 
{ 
var_dump($var); 
echo '<br>THIS VARIABLE IS YET SET<br><br>'; 
}  
}      

$var01a = NULL;
$var01b = 100;
$var01c = array(2, 'alô', 'hello');
$var01d = true;
$var01e = 'Quandoque bonus dormitat Homerus!';
$var01f = M_2_PI;
$var01g = imagecreate(1,2);

class nwteste01
{
var $var1a = 'Isto é um objeto teste';
var $var1b = 'This is a test object';
}
$var01h = new nwteste01;
// echo $var01h->var1a;
// echo $var01h->var1b;

unset($var01b);
@UNsett01($var01b);

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
The @ character before the 
the function name, 
is intended to 
avoid displaying errors 
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

@UNsett01($var01f);

@UNsett01($var01g);

unset($var01h);
@UNsett01($var01h);

?>

EXERCISE


<?php

function UNsett02 ($var) 
{ 
if(!isset($var)) 
{ 
var_dump($var); 
echo '<br>THIS VARIABLE IS UNSET<br><br>'; 
} 
else 
{ 
var_dump($var); 
echo '<br>THIS VARIABLE IS YET SET<br><br>'; 
}  
}      

$var02a = NULL;
$var02b = 100;
$var02c = array(2, 'alô', 'hello');
$var02d = true;
$var02e = 'Quandoque bonus dormitat Homerus!';
$var02f = M_2_PI;
$var02g = imagecreate(1,2);

class nwteste02
{
var $var02h = 'Isto é um objeto teste';
var $var02i = 'This is a test object';
}
$var02j = new nwteste02;
// echo $var02j->var2h . '<br>';
// echo $var02j->var2i . '<br><br>';


unset($var02a, $var02b, $var02c, $var02f, $var02j );

@UNsett02($var02a);

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
The @ character before the 
command for the function, 
is intended to 
avoid displaying errors.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

@UNsett02($var02b);
@UNsett02($var02c);
@UNsett02($var02d);
@UNsett02($var02e);
@UNsett02($var02f);
@UNsett02($var02g);

@UNsett02($var02j);
@UNsett02($var02h);

?>