CODEWITHSUNDEEP
phpoperators
DogBot
DogBot

Reputation: 528

Please explain this php expression "!$variable"

What does an exclamaton mark in front of a variable mean? And how is it being used in this piece of code?

EDIT: From the answers so far I suspect that I also should mention that this code is in a function where one of the parameters is $mytype ....would this be a way of checking if $mytype was passed? - Thanks to all of the responders so far.

 $myclass = null;

    if ($mytype == null && ($PAGE->pagetype <> 'site-index' && $PAGE->pagetype <>'admin-index')) {
        return $myclass;
    }
    elseif ($mytype == null && ($PAGE->pagetype == 'site-index' || $PAGE->pagetype =='admin-index')) {
        $myclass = ' active_tree_node';
        return $myclass;
    }
    elseif (!$mytype == null && ($PAGE->pagetype == 'site-index' || $PAGE->pagetype =='admin-index')) {
        return $myclass;
    }`

Upvotes: 1

Views: 1761

Answers (5)

Fluffeh
Fluffeh

Reputation: 33542

The exclamation mark in PHP means not:

if($var)

means if $var is not null or zero or false while

if(!$var)

means if $var IS null or zero or false.

Think of it as a query along the lines of:

select someColumn where id = 3

and

select someColumn where id != 3

Upvotes: 4

Shail
Shail

Reputation: 1575

!$variable used with If condition to check variable is Null or Not

For example

if(!$var)

means if $var IS null.

Upvotes: 0

Draex_
Draex_

Reputation: 3484

! before variable negates it's value

this statement is actually same as !$mytype since FALSE == NULL

!$mytype == null

statement will return TRUE if $mytype contains one of these:

  • TRUE
  • number other than zero
  • non-empty string

Upvotes: 2

jeremy
jeremy

Reputation: 10057

! negates the value of whatever it's put in front of. So the code you've posted checks to see if the negated value of $mytype is == to null.

return true; //true
return !true; //false

return false; //false
return !false; //true

return (4 > 10); //false
return !(4 < 10); //true

return true == false; //false
return !true == false; //true

return true XOR true; //false
return !true XOR true; //true
return !true XOR true; //false

Upvotes: 3

JRunner
JRunner

Reputation: 1447

elseif (!$mytype == null && ($PAGE->pagetype == 'site-index' || $PAGE->pagetype =='admin-index')) {
    return $myclass;
}

The above !$mytype == null is so wrong. !$mytype means that if the variable evaluates to false or is null, then the condition will execute.

However the extra == null is unnecessary and is basically saying if (false == null) or if (null == null)

Upvotes: 1

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