isset() vs array_key_exists()

isset() vs array_key_exists() in PHP

For most of my PHP career, I’ve used isset() and empty() to determine if an array has a certain key.

But in PHP there are other ways that you can check for variables in arrays, and some of them are also in_array and array_key_exists

In this article, we will cover the difference between isset() and array_key_exists.

isset() is a built-in function in PHP that determines if a variable is set and not null. It returns true if the variable exists and has a value other than null, and false otherwise.

The syntax for isset() is as follows:

isset($var1, $var2, $var3, ...);

array_key_exists() is a built-in function in PHP that is used to check if a specified key or index exists in an array. It returns true if the key/index exists in the array, and false otherwise.

The syntax for array_key_exists() is as follows:

array_key_exists($key, $array);

Note that there are some key differences between these two, for example:

1. isset() is a language construct in PHP that is used to check if a variable is set and not NULL. It can be used to check if an array key exists and has a value.
   array_key_exists(), on the other hand, is a function specifically designed to check if a given key exists in an array, regardless of its value.
2. isset() can be used with both indexed arrays and associative arrays, whereas array_key_exists() is specifically designed to work with associative arrays, i.e., arrays with string keys.
3. isset() is slightly faster than array_key_exists() because it is a language construct in PHP, while array_key_exists() is a built-in function.

A photo is worth a thousand words, an example is worth a thousand photos 😅.

Let’s suppose we have the following array:

$array = [
      'name' => 'Antonio',
      'age' => 32,
      'vip' => false,
      'credits' => 0,
      'city' => '',
      'connections' => null,
      'active' => true,
 ];

And we var_dump() the result, the output would be:

// isset()
'isset($array[name])' => boolean true
'isset($array[age])' => boolean true
'isset($array[vip])' => boolean true
'isset($array[credits])' => boolean true
'isset($array[city])' => boolean true
'isset($array[connections])' => boolean false // <==
'isset($array[active])' => boolean true
'isset($array[missing_key])' => boolean false

// array_key_exists()
'array_key_exists('name', $array)' => boolean true
'array_key_exists('age', $array)' => boolean true
'array_key_exists('vip', $array)' => boolean true
'array_key_exists('credits', $array)' => boolean true
'array_key_exists('city', $array)' => boolean true
'array_key_exists('connections', $array)' => boolean true // <==
'array_key_exists('active', $array)' => boolean true
'array_key_exists('missing_key', $array)' => boolean false

As you can see, for connections key, the isset() and array_key_exists() return different results, because array_key_exists() only checks if the key of the array exists, while the isset() checks that the key exists and has a value different from NULL.

The choice between isset() and array_key_exists() depends on the specific use case and requirements of your code. Here are some guidelines to help you decide when to use each function:

1. Use isset() when you want to check if a variable or an array key is set and not NULL.
2. Use array_key_exists() when you specifically want to check if a given key exists in an associative array, regardless of its value.

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