simple isset question

alcapone

hello there.
I was just wondering if there is any differnce between using these codes:

if(!$something){....}
and
if(!isset($something)){....}

or these:

if($something){....}
and
if(isset($something)){....}

personally I don't see anything different, but just want to be sure.

cheers,
AlCapone

junebug

well, if you use isset() on a variable and it comes back true, then it means that that variable has been set in the script. if you check just to see if it is true or false, you are not able to see if the variable exists in the script.

lets say you have a variable $var in a form. a user uses the form and submits the $var field blank. now, if you use isset() on $var, it will return true because the form passed $var to the script even though it was empty. however, if you check to see if it is true or false, it will be returned false because there is no value in $var.

Anon

Each one has subtle differences.

if(!$something){....}
and
if(!isset($something)){....}

In this one if $something = 0 then the first one will evaluate to true, but if $something is set to anthing else it will evaluate to false. The second statement will only evaluate to true if you've never put anything into the variable $something.

if($something){....}
and
if(isset($something)){....}

In this one your first if will evaluate to true as long as $something != 0. But the second one will evlauate to true as long as anything is in the $something variable.

In both of your questions if you've got your errors set high enough and you try to evaluate on a variable that you've never used PHP will warn you that you are using an undefined variable. isset() is used to keep you from trying to access data that you may not have ever set.

[deleted]

isset() checks if a var has any value assigned to it.

if($var) only checks if $var contains something other than 0 (zero).

If you want to make sure a var is set, always use isset(), NEVER the IF statement.

Thus:
$var = 0;
if (isset($var)) {} // true
if ($var) {} // false

$var = 'hello';
if (isset($var)) {} // true
if ($var) {} // true

unset($var);
if (isset($var)) {} // false
if ($var) {} // false with a great big PHP warning about accessing an unset variable

And ofcourse the same statements with a ! in front of them just give the exact reverse outcome, true becomes false and false becomes true.