Question

What is the best way to define that a value does not exist in PHP, or is not sufficent for the applications needs.

$var = NULL, $var = array(), $var = FALSE?

And what is the best way to test?

isset($var), empty($var), if($var != NULL), if($var)?

Initializing variables as what they will be, e.g. NULL if a string, array() if they will be arrays, has some benefits in that they will function in the setting they are ment to without any unexpected results.

e.g. foreach($emptyArray) won’t complain it just wont output anything, whereas foreach($false) will complain about the wrong variable type.

But it seams like an unnecessary hassle to have so many different ways of doing basically the same thing. eg. if(empty($var)) or if ($var == NULL)

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Duplicate: Best way to test for a variable’s existence in PHP; isset() is clearly broken

Answer 1

Each function you named is for different purposes, and they should be used accordingly:

• empty: tells if an existing variable is with a value that could be considered empty (0 for numbers, empty array for arrays, equal to NULL, etc.).
• isset($var): tells if the script encountered a line before where the variable was the left side of an assignment (i.e. $var = 3;) or any other obscure methods such as extract, list or eval. This is the way to find if a variable has been set.
• $var == NULL: This is tricky, since 0 == NULL. If you really want to tell if a variable is NULL, you should use triple =: $var === NULL.
• if($var): same as $var == NULL.

As useful link is https://www.php.net/manual/en/types.comparisons.php.

The way to tell if the variable is good for a piece of script you’re coding will entirely depend on your code, so there’s no single way of checking it.

One last piece of advice: if you expect a variable to be an array, don’t wait for it to be set somewhere. Instead, initialize it beforehand, then let your code run and maybe it will get overwritten with a new array:

// Initialize the variable, so we always get an array in this variable without worrying about other code. $var = array();  if(some_weird_condition){   $var = array(1, 2, 3); }  // Will work every time. foreach($var as $key => $value){ }