Difference between !== and ==! operator in PHP

In PHP, !== and ==! may look similar but behave very differently. !== is a single operator (strict not-equal), while ==! is actually two operators combined: the equality operator == followed by the logical NOT ! applied to the right operand.

!== (Strict Not-Equal Operator)

The !== operator is a single comparison operator that checks if two values are not equal OR not of the same type. It does not perform type conversion. For example, 1 !== '1' returns true because the types differ (integer vs string).

// !== checks value AND type
var_dump(1 !== '1');    // true (different types)
var_dump(1 !== 1);      // false (same value and type)
var_dump(true !== false); // true (different values)

==! (Two Separate Operators)

==! is not a single operator. PHP interprets it as == (loose equality) followed by ! (logical NOT) applied to the right operand. So $x ==! $y is the same as $x == (!$y).

// ==! is parsed as == (!operand)
// $x ==! $y  is same as  $x == (!$y)
var_dump(true ==! false);  // true == (!false) => true == true => true
var_dump(false ==! true);  // false == (!true) => false == false => true

Key Differences

Example

The following example shows both operators and a case where they produce different results ?

<?php
    $x = true;
    $y = false;

    echo "!== operator: ";
    var_dump($x !== $y);   // true !== false => true

    echo "==! operator: ";
    var_dump($x ==! $y);   // true == (!false) => true == true => true

    // Case where they differ
    $a = 0;
    $b = 1;

    echo "
0 !== 1 : ";
    var_dump($a !== $b);   // true (0 is not identical to 1)

    echo "0 ==! 1 : ";
    var_dump($a ==! $b);   // 0 == (!1) => 0 == false => true (loose)
?>

The output of the above code is ?

!== operator: bool(true)
==! operator: bool(true)

0 !== 1 : bool(true)
0 ==! 1 : bool(true)

Conclusion

!== is a proper strict inequality operator that checks both value and type. ==! is not a real operator − it is == combined with !, meaning "is equal to the negation of." They can produce the same result in some cases but have fundamentally different logic. Always use !== for strict inequality comparisons.