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print_r> <is_unicode
Last updated: Fri, 22 Aug 2008

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isset

(PHP 4, PHP 5)

isset — Determinar si una variable está definida

Descripción

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

Determina si una variable está definida.

Si una variable ha sido removida con unset(), ya no estará definida. isset() devolverá FALSE si prueba una variable que ha sido definida como NULL. También note que un byte NULL ("\0") no es equivalente a la constante NULL de PHP.

Si son pasados varios parámetros, entonces isset() devolverá TRUE únicamente si todos los parámetros están definidos. La evaluación se realiza de izquierda a derecha y se detiene tan pronto como se encuentra una variable definida.

Lista de parámetros

var

La variable a ser revisada.

var

Otra variable ..

...

Valores retornados

Devuelve TRUE si var existe; FALSE de lo contrario.

Ejemplos

Example #1 Ejemplos de isset()

<?php

$var = '';

// Esto evaluará a TRUE así que el texto se imprimirá.
if (isset($var)) {
    echo "Esta variable está definida, así que se imprimirá esto.";
}

// En los siguientes ejemplos usaremos var_dump para imprimir
// el valor devuelto por isset().

$a = "prueba";
$b = "otraprueba";

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

?>

También trabaja con elementos en matrices:

<?php

$a = array ('prueba' => 1, 'hola' => NULL);

var_dump(isset($a['prueba']));         // TRUE
var_dump(isset($a['foo']));            // FALSE
var_dump(isset($a['hola']));           // FALSE

// La clave 'hola' es igual a NULL así que no se considera definida
// Si desea probar por valores NULL en claves, intente:
var_dump(array_key_exists('hola', $a)); // TRUE

?>

Notes

Warning

isset() sólo trabaja con variables, ya que pasar cualquier otra cosa resultará en un error de intérprete. Para chequear si se han definido constantes, use la función defined().

Note: Puesto que esto es una construcción del lenguaje y no una función, no puede ser llamado usando funciones variables

Ver también



print_r> <is_unicode
Last updated: Fri, 22 Aug 2008
 
add a note add a note User Contributed Notes
isset
jwvdveer at gmail dot com
10-Nov-2008 06:29
Here a short note on the function tomek wrote:
Don't use it, because it is still better to use !$var than !is($var).

Some comments on the body of the function:
<?php
function is($var)
{
if (!isset($var)) return false; # Variable is always set... Otherwise PHP would have thrown an error on call.
if ($var!==false) return true; # So, 0, NULL, and some other values may not behave like isNot? And what about the difference between a class and NULL?
return false;
}
?>

The reason why you shall not use this function:
Notice: Undefined variable: {variablename} in {file} on line {__LINE__}

It's me as plain as the nose on your face that the piece of code hasn't been tested with E_NOTICE.

So my advice in this case is: don't use the above function, but simply use !, and functions such like is_null in the situation they are made for.
tomek
26-Oct-2008 02:48
Here's a simple function to test if the variable is set:

<?php
function is($var)
{
if (!isset($var)) return false;
if ($var!==false) return true;
return false;
}
?>

Now instead of very popular (but invalid in many situations):

if (!$var) $var=5;

you can write:

if (!is($var)) $var=5;
a dot schaffhirt at sedna-soft dot de
12-Oct-2008 03:01
You can safely use isset to check properties and subproperties of objects directly. So instead of writing

    isset($abc) && isset($abc->def) && isset($abc->def->ghi)

or in a shorter form

    isset($abc, $abc->def, $abc->def->ghi)

you can just write

    isset ($abc->def->ghi)

without raising any errors, warnings or notices.

Examples
<?php
    $abc = (object) array("def" => 123);
    var_dump(isset($abc));                // bool(true)
    var_dump(isset($abc->def));           // bool(true)
    var_dump(isset($abc->def->ghi));      // bool(false)
    var_dump(isset($abc->def->ghi->jkl)); // bool(false)
    var_dump(isset($def));                // bool(false)
    var_dump(isset($def->ghi));           // bool(false)
    var_dump(isset($def->ghi->jkl));      // bool(false)

    var_dump($abc);                       // object(stdClass)#1 (1) { ["def"] => int(123) }
    var_dump($abc->def);                  // int(123)
    var_dump($abc->def->ghi);             // null / E_NOTICE: Trying to get property of non-object
    var_dump($abc->def->ghi->jkl);        // null / E_NOTICE: Trying to get property of non-object
    var_dump($def);                       // null / E_NOTICE: Trying to get property of non-object
    var_dump($def->ghi);                  // null / E_NOTICE: Trying to get property of non-object
    var_dump($def->ghi->jkl);             // null / E_NOTICE: Trying to get property of non-object
?>
edsko
05-Oct-2008 11:13
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 02:01
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 09:40
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 08:34
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 09:19
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 07:08
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 06:16
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 12:40
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($my_id > 0){
  //why?
}
?>
packard_bell_nec at hotmail dot com
25-Dec-2007 07:18
Note: isset() only checks variables as anything else will result in a parse error. In other words, the following will not work: isset(trim($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 06:51
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 01:51
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 06:22
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 09:50
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 03:31
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 03:30
In PHP 5.2.3, really returns true if the variable is set to null.
black__ray at myway dot com
03-Jul-2007 11:40
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 09:56
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 08:35
"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 06:04
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
29-Nov-2006 11:14
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 06:51
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 05:09
Note that isset() doesnt recognize $_FILES - Arrays.. additionally, i think it doesnt recognize Arrays in general at all (untested, but logical)!
Checking $_FILES will always result in Boolean FALSE i think, at least it caused my Script to calculate false Positives / Negatives... Solution: Use empty() or !empty() :-)
Tee Cee
20-Aug-2006 12:20
In response to 10-Feb-2006 06:02, isset($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 07:13
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 12:26
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 02:08
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. $foo[0]) for it to return the indexed character.
soywiz at php dot net
14-Apr-2006 01:12
Sometimes you have to check if an array has some keys. To achieve it you can use "isset" like this: isset($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 06:27
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 06:02
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 11:06
<?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 07:16
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 10:41
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 07:47
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 07:33
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 06:38
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 08:03
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 03:17
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 03:33
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 12:52
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
01-Mar-2005 11:13
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 06:21
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 02:23
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 10:35
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 06:19
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 09:16
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>";
}
?>
add a note add a note

print_r> <is_unicode
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