Which is the correct syntax for this comparsion operator

Which is the correct syntax for is not equal to operator

this -> !=

if($ses_startdate != $startdate) {
                echo "I am true";
            }

or this -> !==

if($ses_startdate !== $startdate) {
                echo "I am true";
          开发者_开发问答  }

I had been using !== earlier and it worked without any problem but not it is creating the problem with some condition and when i changed it to != it works fine.. why is that?

---

!== is more strict than !=, !== also check the datatype. Examples:

$a = 1;
$b = '1';
$c = 1;
$d = TRUE;
// These are true:
$a == $c;
$a == $b;
$a === $c
$a == $d;
// but these are FALSE:
$a === $b;
$a === $d;

---

$a = '';
$b = false;

if($a != $b)
    //it is not executed since $a and $b are the same (empty) but have different types.

if($a !== $b)
    //it is executed, because $a is a string and $b is boolean, even though both of them represent the same value (empty).

so, the third = tells php to check for the type too.

---

$ses_startdate != $startdate

When doing any comparison which forks your code, get used to doing the equivalent of

var_dump ( $ses_startdate );

var_dump ( $startdate );

Just prior to that condition, dump the values onto the page or put it into your error_logs so you can see what PHP is assessing variables' types and values.