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phpoperator-precedenceexpression-evaluation

Why does !func() <= 30 always evaluate as true?

I'd like to push a "value" into an "array" if the string length is greater than 30. So I have done this PHP script:

if (!mb_strlen($string, 'utf-8') <= 30)
    array_push($array, "value");

But It push that value also if the string is lesser than 31... why?

Solution

  • Why don’t you write the code as you verbalized it?

    mb_strlen($string, 'utf-8') > 30

    The reason why your condition fails is because ! has a higher operator precedence than <=. So !mb_strlen($string, 'utf-8') is evaluated before it is compared to 30, i.e.:

    (!mb_strlen($string, 'utf-8')) <= 30

    And since any number except 0 evaluates to true when converted to boolean, the expression !mb_strlen($string, 'utf-8') is only true for an empty string. And as <= requires the first operand to be numeric, the boolean result of !mb_strlen($string, 'utf-8') is converted to integer where (int)true === 1 and (int)false === 0 and both is alway less than or equal to 30.