Control Structures

User Contributed Notes

11 years ago


For the people that know C: php uses operator short circuit evaluation. That means that as soon as it knows the outcome, it'll stop processing.



<?php

if ( FALSE && some_function() )

    echo "something";

    // some_function() will not be called, since the first operand evaluates to false

?>



This comes in handy for situations like this:



<?php

if ( file_exists($filename) && filemtime($filename) > time() )

    do_something();

    // filemtime will never give a file-not-found-error, since php will stop evaluating if file_exists returns false

?>

Jeffrey

3 years ago


CONTROL STRUCTURE -- BOOLEAN REQUIRED

If you are not sure what will work in your IF statements, try DISECTING your variables. Below I've written three (3) empty CLASS DEFINITIONS (Point, Dimension, and Rectangle), and declared an array called $items that holds all the PHP types you can imagine -- booleans, strings, empty strings, integers, floats, null, arrays, empty arrays, and objects too. The rest of the code really chews up the current $item and spits it out for lunch... Try running this code so you can see the HTML TABLE that is created -- it'll be worth your while.

<?php

class Point { }
class Dimension { }
class Rectangle { }

$items = array(true, false, null, 23, 0, -26, 4.21, 0.0, -3.76,
  'hello', '', array(1, 2, 3), array('', '', ''), array(),
  new stdClass(), new Point(), new Dimension(), new Rectangle());

echo '<table cellpadding="4" border="1">
  <tr>
    <th>syntax</th>
    <th>value</th>
    <th>type</th>
    <th>empty</th>
    <th>boolean</th>
  </tr>' . "\n";

foreach($items AS $item)
{
  $booleanValue = (boolean)$item;
  $empty = (empty($item) ? 'EMPTY' : '&nbsp;');
  $type = gettype($item);
  $syntax = 'if((boolean)';

  $val;

  if($type == boolean)
  {
    $val = ($booleanValue ? 'true' : 'false');
    $syntax .= ($val . ')');
  }
  else if($type == 'NULL')
  {
    $val = 'null';
    $syntax .= 'null)';
  }
  else if($type == double && !$booleanValue)
  {
    $val = '0.0';
    $syntax .= '0.0)';
  }
  else if($type == string)
  {
    $val = '\'' . $item . '\'';
    $syntax .= ($val . ')');
  }
  else if($type == 'array')
  {
    $val = $item;
    $syntax .= '$array)';
  }
  else if($type == 'object')
  {
    $val = get_class($item);
    $syntax .= ('$' . strtolower($val) . ')');
  }
  else
  {
    $val = $item;
    $syntax .= ($val . ')');
  }

  echo '  <tr style="color: ' . ($booleanValue ? '#006600' : '#880000') . ';">
    <td><code>' . $syntax . '</code></td>
    <td>' . $val . '</td>
    <td>' . $type . '</td>
    <td>' . $empty . '</td>
    <td>' . ($booleanValue ? 'TRUE' : 'FALSE') . '</td>
  </tr>' . "\n";
}

echo '</table>' . "\n";

?>

Looking at the HTML output: notice that even integers and floats with a value of zero are considered EMPTY, and all that are EMPTY are FALSE boolean values. And take a gander at the boolean type with a false value... somebody is covering there bases!

wintermute

8 years ago


Sinured: You can do the same thing with logical OR; if the first test is true, the second will never be executed.

<?PHP
if (empty($user_id) || in_array($user_id, $banned_list))
{
exit();
}
?>

Sinured

8 years ago


As mentioned below, PHP stops evaluating expressions as soon as the result is clear. So a nice shortcut for if-statements is logical AND -- if the left expression is false, then the right expression can’t possibly change the result anymore, so it’s not executed.

<?php
/* defines MYAPP_DIR if not already defined */
if (!defined('MYAPP_DIR')) {
    define('MYAPP_DIR', dirname(getcwd()));
}

/* the same */
!defined('MYAPP_DIR') && define('MYAPP_DIR', dirname(getcwd()));
?>

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