A Little Noise

Category: PHP Gotchas

Tricky behavior

  • Connection Conundrum

    Define a user like this:

    GRANT ALL ON *.* TO 'myuser'@'localhost' IDENTIFIED BY 'super$ecret';

    Then try a PHP script like this:

    <?php
    mysqli_connect("localhost", "myuser", "super$ecret");
    ?>

    What happens and why? How could you avoid it?

    And for glory, what single line could you add that would prevent the error, without making any changes to the mysqli_connect line?

  • Static Variable Variables

    <?php
  class A {
    static function b() {
      echo "It works\n";
    }
  }
  $theClass = "A";
  $x = new $theClass;

  /* Are any of the following legal? Which? */

  A::b();
  $x->b();
  $theClass::b();
?>

    Answer: A::b() and $x->b() are legal, $theClass::b() is not.

  • Form Names

    Given the following page:

    <form>
  <input type="radio" name="BT.123" value="active" />
  <input type="radio" name="BT.123" value="inactive" />
  <input type="submit" value="Submit" />
</form>

<?php
  echo "GET: ", $_GET['BT.123'];
  echo "POST: ", $_POST['BT.123'];
  echo "REQUEST: ", $_REQUEST['BT.123'];
?>

    Assume the “inactive” button is checked and the form is submitted. What is the output?
    Answer: Because the “.” is converted to “_”, only the string literals (and some warnings, if using E_STRICT) are output.

    GET: 
POST:
REQUEST:

    In other words, use $_REQUEST[‘BT_123’] instead.

  • Post increment

    <?php
$a = 4;
echo $a+++$a++;
?>

    What is the output?
    Answer: 9. The first $a++ looks up 4, then increments $a. The second $a++ looks up 5, then increments $a. 4 + 5 = 9. $a now contains 6.

  • Concatenate

    What, if anything, is the minimum change (fewest inserted/deleted/modified characters) required to make the output The result is bar:


    <?php
    class A {
      private $foo = "bar";
      public function __toString() {
        return $this->foo;
      }
    }

    $myObject = new A();
    echo "The result is " . $myObject;
    ?>

    Answer:
    echo "The result is " , $myObject;