Very illogical php value comparisons

Question

I stumbled upon a very strange bit of PHP code. Could someone explain why this is happening? *****BONUS POINTS***** if you can tell my why this is useful.

Answer 1

Check out the PHP type comparison tables from the manual. It's a really handy thing to have close at hand until you've internalised it and has been invaluable to my understanding of exactly what will evaluate to true and when.

Others have already answered the core of the question, but I think it's important to state that in PHP, the only non-empty string that does not evaluate to "true" with the == operator is "0" as PHP treats any string containing only numbers as an integer or float.

The rationale for this is that PHP is fairly loosely typed and tries to allow integers, strings, floats and boolean values to be interchangeable. A real-world and extremely common example of this is if you're using the mysql or PDO functions, strings are returned for everything, even if the underlying column is an integer.

Consider the following sql:

CREATE TABLE `test`.`pants` (
`id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`some_other_int` INT NOT NULL
) ENGINE = InnoDB;

INSERT INTO `test`.`pants` (`id`, `some_other_int`)
VALUES ('1', '1'), ('2', '0');

And the following code:

$v) {
        if (!is_string($v))
            echo "field {$v} was not a string!\n";
    }
}

The "field x was not a string!" message is never printed, even though every column in the database is an integer. Suppose you want to actually use the second row in that table.

If the string "0" was not treated as the integer 0 for the comparison, the above code would never print "It was zero!". The programmer would be required to take responsibility for juggling the type of the value which comes out of the database. This is not desirable for a loosely typed language.

Strict equality including type is tested using the "Is really, truly, honest to god equal to" operator, which is represented by the symbol "===".