What does an exclamation mark before a function really mean in PHP

Question

Just as in the title, what does an exclamation mark before a function really mean in PHP?

For example is the following statement:

if (!stripos($haystack, $needle)) {}

the same as this:

if (stripos($haystack, $needle) === FALSE) {}

or this:

if (stripos($haystack, $needle) == FALSE) {}

Any clarification would be appreciated

Solution

The ! preceding the function is the same as...

if (stripos($haystack, $needle) == FALSE) {}

It's the same because it is a == comparison which doesn't check types.

It's called the negation unary operator. It flips the Boolean value (coercing to Boolean if need be) of a value.

For example...

! 0;    // True
! 1 ;   // False
! '';   // True
! true; // False
!! 0    // False 

The !! trick is handy in languages without a (bool) cast. By flipping a value twice, you get the Boolean version of its original value.

Comments

[n1te]

Thanks, this is the clarification I was looking for

[Taha Paksu]

..And thanks for the appreciation. I'm trying to help here. Doesn't my answer make sense to you?

[n1te]

Your answer was good but alex's answer was for me easier to understand. Btw. It wasn't me who voted you down.

[Taha Paksu]

No I was commenting to another comment, sorry. he deleted after I wrote this.

[Pacerier]

@alex, How did you know it coerce to boolean if need be? Did the docs meantion about it? php.net/manual/en/language.operators.logical.php

[user3167101]

@Pacerier It says TRUE if $a is not TRUE.

[Pacerier]

@alex, Why does "is not TRUE" involve coercing? Isn't "is not TRUE" simply !== ?