Question

Possible Duplicate:
php == vs === operator

i have the following code fragment and it doesn’t make sense to me why would NULL be evaluated in 3 different ways. Consider the variable $uploaded_filenames_array as UNKNOWN – we don’t know whether it’s still an array or a NULL. That’s what we are trying to check.

//-----------------------------------------------
if (is_null($uploaded_filenames_array)){
    echo "is_null";
}
else{
    echo "is_NOT_null";
}
//-----------------------------------------------
if ($uploaded_filenames_array == NULL){
    echo "NULL stuff";
}
else{
    echo "not NULL stuff";
}
//-----------------------------------------------
if ($uploaded_filenames_array === NULL){
    echo "NULL identity";
}
else{
    echo "not NULL identity";
}
//-----------------------------------------------

i am getting the following response:

is_NOT_null 
NULL stuff 
not NULL identity 

can somebody help to understand what is the programmatic difference between these 3 ways of checking NULL?

Answer 1

is_null($a) is same as $a === null.

($a === null is bit faster than is_null($a) for saving one function call, but it doesn’t matter, just choose the style you like.)

For the difference of === and ==, read PHP type comparison tables

$a === null be true only if $a is null.

But for ==, the below also returns true.

null == false
null == 0
null == array()
null == ""