the purpose of the unset function

[johnmerlino1]

In C, when you dynamically allocate memory, you have to free it, otherwise you face memory leaks:

char *str;
str = (char *) malloc(10);
free(str);

But in most other languages you do not need to worry about this. PHP has a function called unset, which unsets the variable's value. But why would you want to do this, if PHP has a garbage collector that will free variables once they leave scope anyway? I see no point of unset in a scripting language with garbage collection.

[kicken]

It can be useful as a hint to PHP that the variable is no longer necessary and the memory can be collected. If you're doing something in a loop and might end up reading in a lot of data on a particular iteration adding unset can help get PHP to collect that memory sooner.

 

The primary reason I use it however is to break references, for example if you use a foreach loop with the value as a reference:

foreach ($array as &$value){
  //do stuff
}

After the loop $value will still be a reference to the last item of the array so if you happen to later on do something like:

foreach ($array as $value){
}

you'll end up over-writing the last index with each of the indexes before it. Adding unset($value) after the first loop will prevent this by breaking the reference between $value and the last index.

[davidannis]

I use it to quickly clear part of an array. For example, if I have $myarray['category']['subcategory']['itemtype']['item']

I can

unset($myarray['Honda']['Accord']);

[Zane]

Same as kicken and daviddennis, I usually only find myself using it on array elements.

Edited July 29, 2014 by Zane

[ginerjm]

I find it most useful when I want to remove a session variable.  Obviously php won't clean those up and at times some of them need to be deleted.

[davidannis]

I second ginerjm. It allows me to clear a lot of session data at once without removing all of the session data. For example, on a language learning site I structure $_SESSION as a multi-dimensional array. I have some things like login data that I don't want cleared but I want to clear data on the deck of flashcards that the user is working on. unset ($_SESSION['card_deck']); clears all the data on the flashcards while leaving everything else alone.

[johnmerlino1]

I second ginerjm. It allows me to clear a lot of session data at once without removing all of the session data. For example, on a language learning site I structure $_SESSION as a multi-dimensional array. I have some things like login data that I don't want cleared but I want to clear data on the deck of flashcards that the user is working on. unset ($_SESSION['card_deck']); clears all the data on the flashcards while leaving everything else alone.

So basically unset is the equivalent of setting an initialized value in Java back to null.

[trq]

So basically unset is the equivalent of setting an initialized value in Java back to null.

I don't think so. Unsetting a variable is like it was never initialized at all.

[Jacques1]

C, Java. What language comes next? I suggest Brainfuck.

Edited July 30, 2014 by Jacques1

[ginerjm]

Why are we even debating this?  The OP has to get used to a new environment.  Let's let him get used to it instead of finding fault with every nuance that is 'nu' to him.

Edited July 30, 2014 by ginerjm