How to check if an array element exists

Question

Example  I m checking for the existence of an array element like this   if   self   instances  instanceKey          instances  instanceKey     theInstance      However  I keep getting this error   Notice  Undefined index  test in  Applications MAMP htdocs mysite MyClass php on line 16   Of course  the first time I want an instance   instances will not know the key  I guess my check for available instance is wrong

User · Accepted Answer

You can use either the language construct isset, or the function array_key_exists.

isset should be a bit faster (as it's not a function), but will return false if the element exists and has the value NULL.

For example, considering this array :

$a = array(
    123 => 'glop', 
    456 => null, 
);

And those three tests, relying on isset :

var_dump(isset($a[123]));
var_dump(isset($a[456]));
var_dump(isset($a[789]));

The first one will get you (the element exists, and is not null) :

boolean true

While the second one will get you (the element exists, but is null) :

boolean false

And the last one will get you (the element doesn't exist) :

boolean false

On the other hand, using array_key_exists like this :

var_dump(array_key_exists(123, $a));
var_dump(array_key_exists(456, $a));
var_dump(array_key_exists(789, $a));

You'd get those outputs :

boolean true
boolean true
boolean false

Because, in the two first cases, the element exists -- even if it's null in the second case. And, of course, in the third case, it doesn't exist.

For situations such as yours, I generally use isset, considering I'm never in the second case... But choosing which one to use is now up to you ;-)

For instance, your code could become something like this :

if (!isset(self::$instances[$instanceKey])) {
    $instances[$instanceKey] = $theInstance;
}

User · Answer

You can use the function array key exists to do that   For example    a array  a   gt  Dog   b   gt  Cat    if  array key exists  a   a         echo  Key exists        else       echo  Key does not exist          PS   Example taken from here

User · Answer

A little anecdote to illustrate the use of array key exists      A programmer walked through the parking lot in search of his car    When he neared it  he reached for his pocket to grab his array of keys  keyChain   array       office-door    gt  unlockOffice         home-key    gt  unlockSmallApartment         wifes-mercedes    gt  unusedKeyAfterDivorce         safety-deposit-box    gt  uselessKeyForEmptyBox         rusto-old-car    gt  unlockOldBarrel           He tried and tried but couldn t find the right key for his car    And so he wondered if he had the right key with him     To determine this he used array key exists if  array key exists  rusty-old-car    keyChain         print  Its on the chain

User · Answer

You want to use the array key exists function

User · Answer

array key exists   is SLOW compared to isset    A combination of these two  see below code  would help    It takes the performance advantage of isset   while maintaining the correct checking result  i e  return TRUE even when the array element is NULL   if  isset  a  element       array key exists  element    a              the element exists in the array  write your code here      The benchmarking comparison   extracted from below blog posts    array key exists   only   205 ms isset   only   35ms isset      array key exists     48ms   See  http   thinkofdev com php-fast-way-to-determine-a-key-elements-existance-in-an-array  and  http   thinkofdev com php-isset-and-multi-dimentional-array   for detailed discussion

User · Answer

You can use isset   for this very thing    myArr   array  Name    gt   Jonathan    print  isset  myArr  Name        Exists     Doesn t Exist

User · Answer

You can also use array keys for number of occurrences   lt  php  array array  1   2   6   6   6   5     i count array keys  array  6    if  i gt 0   echo  Element exists in Array     gt

User · Answer

According to the php manual you can do this in two ways  It depends what you need to check   If you want to check if the given key or index exists in the array use array key exists   lt  php  search array   array  first    gt  1   second    gt  4   if  array key exists  first    search array     echo  The  first  element is in the array        gt    If you want to check if a value exists in an array use in array    lt  php   os   array  Mac    NT    Irix    Linux    if  in array  Irix    os     echo  Got Irix       gt

[php] How to check if an array element exists?

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