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[edit] Last updated: Fri, 15 Mar 2013

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isset

(PHP 4, PHP 5)

isset — Determine if a variable is set and is not NULL

Description

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

Determine if a variable is set and is not NULL.

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.

...

Another variable ...

Return Values

Returns TRUE if var exists and has value other than NULL, FALSE otherwise.

Changelog

Version Description
5.4.0

Checking non-numeric offsets of strings now returns FALSE.

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, 'pie' => array('a' => 'apple'));

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

// Checking deeper array values
var_dump(isset($a['pie']['a']));        // TRUE
var_dump(isset($a['pie']['b']));        // FALSE
var_dump(isset($a['cake']['a']['b']));  // FALSE

?>

Example #2 isset() on String Offsets

PHP 5.4 changes how isset() behaves when passed string offsets.

<?php
$expected_array_got_string = 'somestring';
var_dump(isset($expected_array_got_string['some_key']));
var_dump(isset($expected_array_got_string[0]));
var_dump(isset($expected_array_got_string['0']));
var_dump(isset($expected_array_got_string[0.5]));
var_dump(isset($expected_array_got_string['0.5']));
var_dump(isset($expected_array_got_string['0 Mostel']));
?>

Output of the above example in PHP 5.3:

bool(true)
bool(true)
bool(true)
bool(true)
bool(true)
bool(true)

Output of the above example in PHP 5.4:

bool(false)
bool(true)
bool(true)
bool(true)
bool(false)
bool(false)

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.

Note:

When using isset() on inaccessible object properties, the __isset() overloading method will be called, if declared.

See Also

  • empty() - Determine whether a variable is empty
  • __isset()
  • unset() - Unset a given variable
  • defined() - Checks whether a given named constant exists
  • the type comparison tables
  • array_key_exists() - Checks if the given key or index exists in the array
  • is_null() - Finds whether a variable is NULL
  • the error control @ operator



print_rspacer spacer is_string
[edit] Last updated: Fri, 15 Mar 2013
 
spacer add a note User Contributed Notes isset - [52 notes]
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19
muratyaman at gmail dot com
5 years ago
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?
}
?>
up
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14
qeremy
1 year ago
Simple solution for: "Fatal error: Can't use function return value in write context in ..."

<?php
function _isset($val) { return isset($val); }
?>
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10
onno at itmaze dot com dot au ##php==owh
7 years ago
In PHP4, the following works as expected:

<?php
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:

<?php
if (is_array($obj->thing) && isset($obj->thing['key'])) {
  unset($obj->thing['key']) ;
}
?>
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11
Anonymous
6 years ago
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.
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11
beuc at beuc dot net
6 years ago
"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.
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10
phpnet dot 5 dot reinhold2000 at t spamgourmet dot com
7 years ago
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')) [...]
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8
Robert dot VanDell at cbs dot com
3 years ago
Here's a nice little function that I use everywhere that'll help with setting alternate values so you don't have a bunch of situations like:

<?php
if(isset($a))
{
    $b = $a;
}
else
{
    $b = "default";
}

function isset_or(&$check, $alternate = NULL)
{
    return (isset($check)) ? $check : $alternate;
}

// Example usage:
$first_name = isset_or($_POST['first_name'], "Empty");
$total        = isset_or($row['total'], 0);

?>
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8
yaogzhan at gmail dot com
7 years ago
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'.
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8
contact at scottbyrns dot com
5 years ago
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($len > 0){
            return true;
        }
        else{
            return false;
        }
    }
    else{
        return false;
    }
}
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7
packard_bell_nec at hotmail dot com
5 years ago
Note: isset() only checks variables as anything else will result in a parse error. In other words, the following will not work: isset(trim($name)).

isset() is the opposite of is_null($var) , except that no warning is generated when the variable is not set.
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7
soapergem at gmail dot com
4 years ago
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 fa
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