print_r

is_unicode

Last updated: Fri, 26 Sep 2008

isset

(PHP 4, PHP 5)

isset — Determine whether a variable is set

Description

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

Determine whether a variable is set.

If a variable has been unset with unset(), it will no longer be set. isset() will return FALSE if testing a variable that has been set to NULL. Also note that a NULL byte ("\0") is not equivalent to the PHP NULL constant.

If multiple parameters are supplied then isset() will return TRUE only if all of the parameters are set. Evaluation goes from left to right and stops as soon as an unset variable is encountered.

Parameters

var: The variable to be checked.
var: Another variable ..
...

Return Values

Returns TRUE if var exists; FALSE otherwise.

Examples

Example #1 isset() Examples


<?php

$var = '';

// This will evaluate to TRUE so the text will be printed.
if (isset($var)) {
    echo "This var is set so I will print.";
}

// In the next examples we'll use var_dump to output
// the return value of isset().

$a = "test";
$b = "anothertest";

var_dump(isset($a));      // TRUE
var_dump(isset($a, $b)); // TRUE

unset ($a);

var_dump(isset($a));     // FALSE
var_dump(isset($a, $b)); // FALSE

$foo = NULL;
var_dump(isset($foo));   // FALSE

?>

This also work for elements in arrays:


<?php

$a = array ('test' => 1, 'hello' => NULL);

var_dump(isset($a['test']));            // TRUE
var_dump(isset($a['foo']));             // FALSE
var_dump(isset($a['hello']));           // FALSE

// The key 'hello' equals NULL so is considered unset
// If you want to check for NULL key values then try: 
var_dump(array_key_exists('hello', $a)); // TRUE

?>

Notes

Warning

isset() only works with variables as passing anything else will result in a parse error. For checking if constants are set use the defined() function.

Note: Because this is a language construct and not a function, it cannot be called using variable functions


It has been remarked by various people that isset is the opposite of is_null "in all but buggy cases". This is not true:



<?php

  $str = "hi";

  var_dump(isset($str[1]));

  var_dump(@!is_null($str[1]));

  var_dump(isset($str[2]));

  var_dump(@!is_null($str[2]));

?>



outputs



bool(true)

bool(true)

bool(false)

bool(true)

mark dot fabrizio at gmail dot com
16-Sep-2008 04:01


I know this is probably not the recommended way to do this, but it seems to work fine for me. Instead of the normal isset check to extract variables from arrays (like $_REQUEST), you can use the @ prefix to squelch any errors.



For example, instead of:

<?php

$test = isset($_REQUEST['test']) ? $_REQUEST['test'] : null;

?>

you can use:

<?php

$test = @$_REQUEST['test'];

?>



It saves some typing, but doesn't give the opportunity to provide a default value. If 'test' is not an assigned key for $_REQUEST, the assigned value will be null.

mandos78 AT mail from google
29-Jul-2008 11:40


Careful with this function "ifsetfor" by soapergem, passing by reference means that if, like the example $_GET['id'], the argument is an array index, it will be created in the original array (with a null value), thus causing posible trouble with the following code. At least in PHP 5.



For example:



<?php

$a = array();

print_r($a);

ifsetor($a["unsetindex"], 'default');

print_r($a);

?>



will print 



Array

(

)

Array

(

    [unsetindex] => 

)



Any foreach or similar will be different before and after the call.

soapergem at gmail dot com
02-Jul-2008 10:34


It is possible to encapsulate isset() calls inside your own functions if you pass them by reference (note the ampersand in the argument list) instead of by value. A prime example would be the heavily-requested "ifsetor" function, which will return a value when it is set, otherwise a default value that the user specifies is used.



<?php



function ifsetor(&$val, $default = null)

{

    return isset($val) ? $val : $default;

}



//    example usage

$id = intval(ifsetor($_GET['id'], 0));



?>

soapergem at gmail dot com
04-Jun-2008 11:19


Below a user by the name of Scott posted an isval() function; I just wanted to point out a revision to his method since it's a bit lengthy for what it does. The trick is to realize that a boolean AND clause will terminate with false as soon as it encounters anything that evaluates to false, and will skip over any remaining checks.



Instead of taking up the space to define isval(), you could just run inline commands for each variable you need to check this:



<?php



$isval = isset($_POST['var']) && !empty($_POST['var']);



?>



Also be warned that if you try to encapsulate this into a function, you might encounter problems. It's meant to stand alone.

John A. Bilicki III
10-Mar-2008 08:08


I was attempting to use isset to detect if a class existed or not and kept having an error...



Call to a member function get() on a non-object...



For example I have some pages where I want to disable my own error reporting for non-existent HTTP queries. The HTTP query error handling file was merely included in my templates though now I can declare a class that uses that template system, declare an error class, and have the template system not serve the error handling when I will be using a large array of queries that I will not be tracking...

<?php if (!class_exists('error')) {include("includes.php");} ?>

anonymousleaf at gmail dot com
25-Feb-2008 07:16


isset expects the variable sign first, so you can't add parentheses or anything.



<?php

    $foo = 1;

    if(isset(($foo))) { // Syntax error at isset((

        $foo = 2;

    }

?>

muratyaman at gmail dot com
07-Feb-2008 01:40


To organize some of the frequently used functions..



<?php



/**

 * Returns field of variable (arr[key] or obj->prop), otherwise the third parameter

 * @param array/object $arr_or_obj

 * @param string $key_or_prop

 * @param mixed $else

 */

function nz($arr_or_obj, $key_or_prop, $else){

  $result = $else;

  if(isset($arr_or_obj)){

    if(is_array($arr_or_obj){

      if(isset($arr_or_obj[$key_or_prop]))

        $result = $arr_or_obj[$key_or_prop];

    }elseif(is_object($arr_or_object))

      if(isset($arr_or_obj->$key_or_prop))

        $result = $arr_or_obj->$key_or_prop;

    }

  }

  return $result;

}



/**

 * Returns integer value using nz()

 */

function nz_int($arr_or_obj, $key_or_prop, $else){

  return intval(nz($arr_or_obj, $key_or_prop, $else));

}



$my_id = nz_int($_REQUEST, 'id', 0);

if($my_id > 0){

  //why?

}

?>

packard_bell_nec at hotmail dot com
25-Dec-2007 08:18


Note: isset() only checks variables as anything else will result in a parse error. In other words, the following will not work: isset(trim($name)). 



isset() is the opposite of is_null($var) , except that no warning is generated when the variable is not set.

sam b
13-Nov-2007 07:51


Check out this ifsetor function. If $var is set, do nothing, otherwise $var = $default.



<?php



$name = ifsetor($name, 'default name') ;



function ifsetor(&$var, $default)

    {

        return isset($var) ? $var : $default) ;

    }

    

?>

contact at scottbyrns dot com
08-Nov-2007 02:51


If you have for example a variable in your URL say url.php?var= and some one types in %00 the variable will pass isset. For post and get variables I wrote this function to filter out varables that are set but empty.



function isval($inp){

    if(isset($inp)){

        $len = strlen($inp);

        if($len > 0){

            return true;

        }

        else{

            return false;

        }

    }

    else{

        return false;

    }

}

petruzanauticoyahoo?com!ar
14-Oct-2007 08:22


I've come up with a little not-so-clean but useful function to avoid checking if a variable is set before reading its value, specially useful for $_REQUEST and the like:



<?php

function toLocal( $source, &$dest, $default = null )

{

    if( isset( $source ) )

        $dest = $source;

    else

        $dest = $default;

}

?>



and then call it this way:

<?php

@toLocal( $_REQUEST['item_id'], $item_id, 0 );

?>



It checks wether the variable is set, copies it to a local variable, and if it wasn't set, it assigns the new variable a default value, all in one line, preventing you to have to always check for isset() before trying to read its value.

Gotta call it with @ because if the variable is not set, then trying to pass it as an argument will yield a warning.



Petruza.

phpnotes dot 20 dot zsh at spamgourmet dot com
22-Sep-2007 11:50


Note that isset is lazy -- the first undefined variable causes it to return. Have a look at this example:



<?php

class Foo {

    public function __isset($varname) {

        echo "ZOMG! isset was called on my $varname!\n";

    }

}

$foo = new Foo;

// bar will never get checked

var_dump(isset($foo->foo, $foo->bar));



// Output:

// ZOMG! isset was called on my foo!

// bool(false)

?>

codeslinger at compsalot dot com
14-Aug-2007 05:31


The behavior of isset is complex and the results are sometimes not what people expected -- to their peril.



After dealing with isset() for awhile and peppering my code with additional checks for edge cases.  I eventually got to know and love  empty()



Most of the places that you are using isset(), empty() would do a better job.



And when you are dealing with arrays what you probably want to use instead of isset() is   array_key_exists()



These days, I almost never use isset() and I write a lot of code.

talbutt(at)mail(dot)med(dot)upenn(edu)
13-Aug-2007 05:30


In PHP 5.2.3, really returns true if the variable is set to null.

black__ray at myway dot com
03-Jul-2007 01:40


if(isset($_POST['in_qu']))

          {



          include("qanda/in_qu.php");

          $content.=$message;

          include("qanda/view_qanda.php");

    }

elseif(isset($_GET['rq']))

          {

          include("qanda/add_answer.php");

    }

elseif(isset($_POST['add_answer']))

          {

          include("qanda/in_an.php");

          $content.=$message;

          include("qanda/view_qanda.php");

    }

elseif($_GET['act']== 'v_qanda' && !(isset($_GET['rq'])))

{

include("qanda/view_qanda.php");

}

/*

if(isset($_POST['add_answer']))

beuc at beuc dot net
01-Jan-2007 10:56


Beware that the chk() function below creates the variable or the array index if it didn't existed.



<?php

function chk(&$var) {

  if (!isset($var))

    return NULL;

  else

    return $var;

}



echo '<pre>';

$a = array();

var_dump($a);

chk($a['b']);

var_dump($a);

echo '</pre>';



// Gives:

// array

//   empty

// 

// array

//   'b' => null

?>

beuc at beuc dot net
16-Dec-2006 09:35


"empty() is the opposite of (boolean) var, except that no warning is generated when the variable is not set."



So essentially

<?php

if (isset($var) && $var)

?>

is the same as

<?php

if (!empty($var))

?>

doesn't it? :)



!empty() mimics the chk() function posted before.

roberto at spadim dot com dot br
04-Dec-2006 07:04


test:



<?php

$qnt=100000;

$k=array();

for ($i=0;$i<$qnt;$i++)

$k[$i]=1;



echo microtime()."\n";

for ($i=0;$i<$qnt;$i++)if(isset($k[$i]));

echo microtime()."\n";

for ($i=0;$i<$qnt;$i++)if(array_key_exists($i,$k));

echo microtime()."\n";

for ($i=0;$i<$qnt;$i++)if($k[$i]==1);

echo microtime()."\n";



?>



the interesting result:

isset is the fastest

php at bagnara dot org
30-Nov-2006 12:14


See also property_exists() which allows detection of protected variables existing in a class even if they are NULL.

randallgirard at hotmail dot com
27-Sep-2006 08:51


The unexpected results of isset has been really frustrating to me. Hence, it doesn't work how you'd think it would, (as documented) a var currently in the scope with a null value will return false.





Heres a quick solution, perhaps there are better ways of going about this, but heres my solution...





<?php


function is_set( $varname, $parent=null ) {


  if ( !is_array( $parent ) && !is_object($parent) ) {


    $parent = $GLOBALS;


  }


  return array_key_exists( $varname, $parent );


}


?>





Hence, $varname should be a mixed value of var's to check for, and $parent can be an array or object, which will default to the GLOBAL scope. See the documentation of array_key_exists for further information.





This will allow to check if a var is in the current scope, object, or array... Whether it's a null, false, true, or any value. It depends on ARRAY_KEY_EXISTS for it's functionality which also works with Objects. Feel free to improve on this anyone ;D

DerSpezialist at Hotmail dot com
29-Aug-2006 07:09


Note that isset() doesnt recognize $_FILES - Arrays.. additionally, i think it doesnt recognize Arrays in general at all (untested, but logical)!

Checking $_FILES will always result in Boolean FALSE i think, at least it caused my Script to calculate false Positives / Negatives... Solution: Use empty() or !empty() :-)

Tee Cee
20-Aug-2006 02:20


In response to 10-Feb-2006 06:02, isset($v) is in all (except possibly buggy) cases equivalent to !is_null($v). And no, it doesn't actually test if a variable is set or not by my definition "$v is set if unset($v) has no effect".



<?php

unset($c); //force $c to be unset

var_dump($a=&$c); // NULL, but this actually sets $a and $c to the 'same' NULL.

var_dump(isset($c)); // bool(false)

var_dump($a = 5); // int(5)

var_dump($c); // int(5)



unset($c);

var_dump($a=&$c); // NULL

var_dump(isset($c)); // bool(false)

unset($c);

var_dump($a = 5); // int(5)

var_dump($c); // NULL

?>



In the following example, we see an alternate method of testing if a variable is actually set or not:

<?php

var_dump(array_key_exists('c',get_defined_vars())); // false 

var_dump(isset($c));                                // also false

var_dump($c);                                       // manipulate $c a bit...

var_dump((string)$c);

var_dump(print_r($c,true));

var_dump($a=$c);

var_dump(array_key_exists('c',get_defined_vars())); // ... still false

var_dump($c = NULL);                                // this sets $c

var_dump(array_key_exists('c',get_defined_vars())); // true!

var_dump(isset($c));                                // false; isset() still says it's unset

unset($c);                                          // actually unset it

var_dump(array_key_exists('c',get_defined_vars())); // false

var_dump($a=&$c);                                           

var_dump(array_key_exists('c',get_defined_vars())); // true!

unset($c);                                          // unset it again

var_dump(&$c);                                      // &NULL

var_dump(array_key_exists('c',get_defined_vars())); // true!

?>



Obviously, null values take up space (or they wouldn't show up in get_defined_vars). Also, note that &$v sets $v to NULL if it is unset.

purpleidea
17-Aug-2006 09:13


fyi:


you *cannot* do assignments inside of the isset() function. although you *can* while inside of other functions such as is_null().





<?php


if (isset($var = $_GET['key'])) echo 'whatever'; //this will throw an error :(





if (is_null($var = $_GET['key'])) echo 'whatever'; //this will not :)


?>





hope someone finds this useful.

ludie-at-vibage-punkt-kom
16-Aug-2006 02:26


If you don't want to bother checking every single var with isset or empty, use this function on every var you use:



<?php



function chk( & $var )

{

    if ( !isset($var) )

    {

        return NULL;

    }

    else

    {

        return $var;

    }

}



?>



It takes ANYTHING as argument, and returns the exact same thing, but without Notice if the var doesn't actually exist

21-Jul-2006 04:08


I tried the example posted previously by Slawek:



$foo = 'a little string';

echo isset($foo)?'yes ':'no ', isset($foo['aaaa'])?'yes ':'no ';



He got yes yes, but he didn't say what version of PHP he was using.



I tried this on PHP 5.0.5 and got:  yes no



But on PHP 4.3.5 I got:  yes yes



Apparently, PHP4 converts the the string 'aaaa' to zero and then returns the string character at that position within the string $foo, when $foo is not an array. That means you can't assume you are dealing with an array, even if you used an expression such as isset($foo['aaaa']['bbb']['cc']['d']), because it will return true also if any part is a string.



PHP5 does not do this. If $foo is a string, the index must actually be numeric (e.g. $foo[0]) for it to return the indexed character.

soywiz at php dot net
14-Apr-2006 03:12


Sometimes you have to check if an array has some keys. To achieve it you can use "isset" like this: isset($array['key1'], $array['key2'], $array['key3'], $array['key4'])

You have to write $array all times and it is reiterative if you use same array each time.



With this simple function you can check if an array has some keys:



<?php

function isset_array() {

    if (func_num_args() < 2) return true;

    $args = func_get_args();

    $array = array_shift($args);

    if (!is_array($array)) return false;

    foreach ($args as $n) if (!isset($array[$n])) return false;

    return true;

}

?>



Use: isset_array($array, 'key1', 'key2', 'key3', 'key4')

First parameter has the array; following parameters has the keys you want to check.

kariedoo
09-Mar-2006 07:27


Before:



//ask, if is set

$number = isset($_GET['number']) ? $_GET['number'] : '';

$age = isset($_GET['age']) ? $_GET['age'] : '';

$street = isset($_GET['street']) ? $_GET['street'] : '';



After: --> it's easier to read



//ask, if is set

 $parameter = array('number', 'age', 'street');

 foreach($parameter as $name)

 {

    $$name = isset($_GET[$name]) ? $_GET[$name] : '';

 }

red at iklanumum dot com
10-Feb-2006 07:02


This could be viewed as a philosophy. I wonder why a NULL variabel is being considered FALSE rather than TRUE while in isset, because if the variable has been unset it becomes undefined but a NULL variabel is still defined although it has no value. Or, perhaps, it's based on the memory usage, if it is how about $x="" ? Is empty value use memory too? This leads me to another thinking that the isset isn't have family relationship with unset although both of it are a language construct and have 'set' word :)

Slawek Petrykowski
29-Nov-2005 12:06


<?php

$foo = 'a little string';

echo isset($foo)?'yes ':'no ', isset($foo['aaaa'])?'yes ':'no ';

>



results with unexpected values:

yes yes



Well, it is necessary to check type of $foo first !

Peter Beckman <beckman at purplecow dot com>
21-Sep-2005 09:16


Based on the previous post, I've found this code even more useful:



<?php

function isset_sum(&$var, $val) {

    if (isset($var))  $var += $val;

    else              $var  = $val;

}

?>



Now instead of:



<?php 

if (isset($foo[$bar][$baz][$fooz])) $foo[$bar][$baz][$fooz] += $count;

else                                $foo[$bar][$baz][$fooz] = $count;

?>



No more "Undefined variable" warnings, and you save your fingers and sanity!  Thanks to the previous poster for inspiration.

14-Sep-2005 12:41


I don't know if you guys can use this but i find this piece of code pretty useful (for readabillity at least):



function isset_else( $&v, $r )

{

    if( isset( $v ))

        return $v;

    else

        return $r;

}



This way you can go:



$a = 4;



$c += isset_else( $a, 0 );

$c += isset_else( $b, 0 );



echo $c;



Of course, this code would work anyway, but you get the point.

php [at] barryhunter [.] co [.] uk
07-Sep-2005 09:47


In case it helps someone, here's a table to compare different Variable tests/comparisons



http://www.deformedweb.co.uk/php_variable_tests.php

onno at itmaze dot com dot au ##php==owh
12-Aug-2005 09:33


In PHP4, the following works as expected:



if (isset($obj->thing['key'])) {

  unset($obj->thing['key']) ;

}



In PHP5 however you will get a fatal error for the unset().



The work around is:



if (is_array($obj->thing) && isset($obj->thing['key'])) {

  unset($obj->thing['key']) ;

}

richard william lee AT gmail
11-Jun-2005 08:38


Just a note on the previous users comments. isset() should only be used for testing if the variable exists and not if the variable containes an empty "" string. empty() is designed for that.



Also, as noted previosuly !empty() is the best method for testing for set non-empty variables.

darkstar_ae at hotmail dot com
25-May-2005 10:03


isset doesn't reliably evaluate variables with blank strings (not necessarily NULL).

i.e.

$blankvar = ""; // isset will return true on this. 



This is a very common pitfall when handling HTML forms that return blank text fields to the script. You're better off doing this:



if ($var != "")

return true;

else

return false;



This more of a programming practice rather than the function's shortcomings. So if you have a habit of initializing variables you're likely to run into problems with isset() if your code or php project become very large.

Andrew Penry
11-May-2005 05:17


The following is an example of how to test if a variable is set, whether or not it is NULL. It makes use of the fact that an unset variable will throw an E_NOTICE error, but one initialized as NULL will not. 



<?php



function var_exists($var){

    if (empty($GLOBALS['var_exists_err'])) {

        return true;

    } else {

        unset($GLOBALS['var_exists_err']);

        return false;

    }

}



function var_existsHandler($errno, $errstr, $errfile, $errline) {

   $GLOBALS['var_exists_err'] = true;

}



$l = NULL;

set_error_handler("var_existsHandler", E_NOTICE);

echo (var_exists($l)) ? "True " : "False ";

echo (var_exists($k)) ? "True " : "False ";

restore_error_handler();



?>



Outputs:

True False



The problem is, the set_error_handler and restore_error_handler calls can not be inside the function, which means you need 2 extra lines of code every time you are testing. And if you have any E_NOTICE errors caused by other code between the set_error_handler and restore_error_handler they will not be dealt with properly. One solution:



<?php



function var_exists($var){

   if (empty($GLOBALS['var_exists_err'])) {

       return true;

   } else {

       unset($GLOBALS['var_exists_err']);

       return false;

   }

}



function var_existsHandler($errno, $errstr, $errfile, $errline) {

    $filearr = file($errfile);

    if (strpos($filearr[$errline-1], 'var_exists') !== false) {

        $GLOBALS['var_exists_err'] = true;

        return true;

    } else {

        return false;

    }

}



$l = NULL;

set_error_handler("var_existsHandler", E_NOTICE);

echo (var_exists($l)) ? "True " : "False ";

echo (var_exists($k)) ? "True " : "False ";

is_null($j);

restore_error_handler();



?>



Outputs:

True False

Notice: Undefined variable: j in filename.php on line 26



This will make the handler only handle var_exists, but it adds a lot of overhead. Everytime an E_NOTICE error happens, the file it originated from will be loaded into an array.

phpnet dot 5 dot reinhold2000 at t spamgourmet dot com
10-Apr-2005 05:33


if you want to check whether the user has sent post vars from a form, it is a pain to write something like the following, since isset() does not check for zero-length strings:



if(isset($form_name) && $form_name != '') [...]



a shorter way would be this one:



if($form_name && $form_message) [...]



but this is dirty since you cannot make sure these variables exist and php will echo a warning if you refer to a non-existing variable like this. plus, a string containing "0" will evaluate to FALSE if casted to a boolean.



this function will check one or more form values if they are set and do not contain an empty string. it returns false on the first empty or non-existing post var.



<?

function postvars() {

    foreach(func_get_args() as $var) {

        if(!isset($_POST[$var]) || $_POST[$var] === '') return false;

    }

    return true;

}

?>



example: if(postvars('form_name','form_message')) [...]

yaogzhan at gmail dot com
20-Mar-2005 01:52


in PHP5, if you have 



<?PHP

class Foo

{

    protected $data = array('bar' => null);



    function __get($p)

    {

        if( isset($this->data[$p]) ) return $this->data[$p];

    }

}

?>



and

<?PHP

$foo = new Foo;

echo isset($foo->bar);

?>

will always echo 'false'. because the isset() accepts VARIABLES as it parameters, but in this case, $foo->bar is NOT a VARIABLE. it is a VALUE returned from the __get() method of the class Foo. thus the isset($foo->bar) expreesion will always equal 'false'.

dubmeier aaattt Y! daht calm
02-Mar-2005 12:13


Here are some handy wrappers to isset that I use when I need to do common evaluations like: this variable is set and has a length greater than 0, or: I want the variables value, or a blank, if not set.



/**

 * isset_echo()

 * 

 * Accomplishes the following w/o warnings:

 *    echo $x;

 *    echo $x[$y];

 *    echo $x[$y][$z];

 *

 * FIXME: make this recursive so it works for N args?

 */

function isset_echo($x, $y=Null, $z=Null)

{

    if (is_array($x)) {

        if (array_key_exists($y, $x)) {

            if (is_array($x[$y])) {

                if (array_key_exists($z, $x[$y])) { echo $x[$y][$z]; }

            }

            else { echo $x[$y]; }

        }

    }

    else { echo $x; }

}



/**

 * isset_value()

 * 

 * As above, but returns value instead of echoing

 */

function isset_value(&$x, $y=Null)

{

    if (is_array($x)) {

        if (array_key_exists($y, $x)) { return $x[$y]; }

    }

    else { return $x; }

}



/**

 * isset_and_equals()

 *

 * As above, but ...

 * Returns true if variable (or array member) is set and equaL to the first parameter

 */

function isset_equals($val, $w, $x=null, $y=null, $z=null) {

    if (is_array($w)) {

                if (array_key_exists($x, $w)) {

                if (is_array($w[$x])) {

                        if (array_key_exists($y, $w[$x])) {

                                    if (is_array($w[$x][$y])) {

                                        if(array_key_exists($z, $w[$x][$y])) {

                                                return ($w[$x][$y][$z] == $val) ? true : false;

                                        }

                                    } else {

                                        return ($w[$x][$y] == $val) ? true : false;

                                    }

                            }

                    } else {

                        return ($w[$x] == $val) ? true : false;

                    }

        }

    } else { 

                return ($w == $val) ? true : false;

        }

}



/**

 * isset_gt0()

 * 

 * As above, but returns true only if var is set and it's length is > 0

 */

function isset_gt0(&$x)

{

    if (isset($x) && strlen($x) > 0) { return true; }

    else { return false; }

}

codeslinger at compsalot dot com
07-Feb-2005 07:21


according to the docs -- "isset() will return FALSE if testing a variable that has been set to NULL."



That statment is not always correct, sometimes isset() returns TRUE for a NULL value.  But the scenarios are obtuse.  There are a tons of bugs on this subject, all marked as bogus.



Problems occur when NULLs are in named fields of arrays and also when vars are passed by reference.



do lots of testing and code defensively.



is_null()   is your friend...

pianistsk8er at gmail dot com
10-Dec-2004 03:23


This function is very useful while calling to the URL to specify which template to be used on certain parts of your application.



Here is an example...



<?php



    $cat = $_GET['c'];

    $id = $_GET['id'];    

    $error = 'templates/error.tpl';



    if( isset($cat))

    {

        if( isset($id))

        {

            $var = 'templates/pics/' . $cat . '-' . $id . '.tpl';

            if (is_file($var))

            {

                include($var);

            }

            else

            {

                include($error);

            }

        }

        else

        {

            $var = 'templates/pics/' . $cat . '.tpl';        

            if (is_file($var))

            {

                include($var);

            }

            else

            {

                include($error);

            }

        }

    }

    else

    {

        include('templates/alternative.'.tpl);

    }



?>



You can see several uses of the isset function being used to specify wheter a template is to be called upon or not.  This can easily prevent other generic PHP errors.

jc dot michel at symetrie dot com
15-Nov-2004 11:35


Using

  isset($array['key']) 

is useful, but be careful!

using 

  isset($array['key']['subkey']) 

doesn't work as one could expect, if $array['key'] is a string it seems that 'subkey' is converted to (integer) 0 and $array['key']['subkey'] is evaluated as the first char of the string. 

The solution is to use 

  is_array($array['key']) && isset($array['key']['subkey'])



Here is a small code to show this:



<?php

$ex = array('one' => 'val1','two' => 'val2');

echo '$ex = ';print_r($ex);

echo "<br />";



echo " isset(\$ex['one']['three']) : ";

if (isset($ex['one']['three']))

    echo 'true';

else

    echo 'false';



echo "<br />";

echo "is_array(\$ex['one']) &&  isset(\$ex['one']['three']) : ";

if (is_array($ex['one']) && isset($ex['one']['three']))

    echo 'true';

else

    echo 'false';

?>



shows:

$ex = Array ( [one] => val1 [two] => val2 )

isset($ex['one']['three']) : true

is_array($ex['one']) && isset($ex['one']['three']) : false

jon
07-Dec-2003 07:19


Since PHP will check cases in order, I often end up using this bit of code:



<?php

if (isset($var) && $var) {

    // do something

}

?>



In short, if you have error reporting on, and $var is not set, PHP will generate an error if you just have:



<?php 

if ($var) { // do something }

?>



...but, as noted elsewhere, will return True if set to False in this case:

<?php

if (isset($var)) { // do something }

?>



Checking both to see if $var is set, and that it equals something other than Null or False is something I find very useful a lot of times.  If $var is not set, PHP will never execute the second part of "(isset($var) && $var)", and thus never generate an error either.



This also works very nice for setting variable as well, e.g.:

<?php

$var = (isset($var) && $var) ? $var : 'new value';

?>

flobee at gmx dot net
08-Sep-2003 11:16


just as note: if you want to check variables by boolean value: true or false , "isset" has a different meaning!

<?php

$var=null;

// sample 1

if($var) {

   // if true or another value exept "false" , "null": go on here

   echo "1. var is true or has a value $var<br>";

} else {

   echo "1. var is &quot;false&quot; or &quot;null&quot;<br>";

}



if(!$var) {

   // if false or "null": go on here

   echo "2. var has no value $var<br>";

} else {

   echo "2. var is &quot;false&quot; or &quot;null&quot;<br>";

}



// sample 2

$var =false;

if(isset($var)) {

  // $var is false so it is set to a value and the execution goes here

   echo "3. var has value: $var<br>";

}



$var=null;

if(!isset($var)) {

  // $var is null (does not exist at this time) and the execution goes here

   echo "4. var was not set $var<br>";

}

?>

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