PHP: Associative Arrays II

Derek Bridge

Department of Computer Science,
University College Cork

PHP: Associative Arrays II

Aims:

• to learn some of PHP's built-in functions for processing associative arrays
• to practice writing PHP for processing associative arrays

Built-in functions

• Some of PHP's 70+ built-in functions for array processing are for associative arrays
• count( $a ) (and sizeof) can be used on associative arrays as well as indexed arrays
• array_key_exists( $k, $a ) returns true if $k is one of the keys in associative array $a, otherwise returns false
• isset( $variable ):
  Rather than
  if ( array_key_exists('Jujubes', $fruit_prices) ) ...
  PHP programmers are more likely to write
  if ( isset($fruit_prices['Jujubes']) ) ...
  These are the same except
  • the former returns true when $fruit_prices contains a key/value pair where the key is 'Jujubes' and the value is NULL
  • the latter returns false in this case
• array_keys( $a ) returns an array containing just the keys in associative array $a (usually in the order in which they were inserted)
• array_values( $a ) returns an array containing just the values in associative array $a (usually in the order in which they were inserted)

Class exercise: what is the output of the following?

$month_lengths = array('Jan' => 31, 'Feb' => 28,
    'Mar' => 31, 'Apr' => 30, 'May' => 31, 'Jun' => 30, 'Jul' => 31, 
    'Aug' => 31, 'Sep' => 30, 'Oct' => 31, 'Nov' => 31, 'Dec' => 31);

if ( array_key_exists( 'Mar', $month_lengths ) )
{
    echo '<p>Beware the Ides of March</p>';
}
if ( isset($month_lengths['Mar']) )
{
    echo '<p>The Ides of March are come</p>';
}

if ( array_key_exists( 'April', $month_lengths ) )
{
    echo '<p>April is the cruelest month</p>';
}
if ( isset($month_lengths['April']) )
{
    echo '<p>Drip, drip, drop, little April showers</p>';
}

$months = array_keys($month_lengths);
foreach ($months as $month)
{
    echo "<p>{$month}</p>";
}

foreach (array_values($month_lengths) as $length)
{
    echo "<p>{$length}</p>";
}

Class exercise

• In the previous lecture, we saw some PHP for outputting the $module_lecturers array as a table, one row per key/value (see left-hand table below)

  echo "<table>";
  foreach ($module_lecturers as $module => $lecturer) 
  {
      echo "<tr>";
      echo "<td>{$module}</td>";
      echo "<td>{$lecturer}</td>";
      echo "</tr>";
  }
  echo "</table>";

• Write PHP that outputs the array as a table, but with one column per key/value (see right-hand table below)

  AL1101	Hugh Jeegoh
  WC1101	Ann O Domini

  AL1101	WC1101
  Hugh Jeegoh	Ann O Domini

$_GET is an associative array

• Suppose form.html contains this form:

  <form action="process.php" method="get">
      <input type="text" name="firstname" />
      <input type="text" name="surname" />
      <input type="submit" />
  </form>

• Suppose the user enters 'Hugh' and 'Jeegoh' and presses Submit
• The browser sends this request
  GET process.php?firstname=Hugh&surname=Jeegoh
• The PHP script, process.php, contains something like this to access the user's data:

  $firstname = $_GET['firstname'];
  $surname = $_GET['surname'];

• PHP automatically creates for us an associative array called $_GET
• Class exercise: What are the keys and values in this example and where did they come from?

PHP's superglobals

• PHP creates 6 associative arrays for us, referred to as superglobal variables
• (No need to memorize) They contain the EGPCS information (environment, GET, POST, cookies and server), and information about files
  • $_ENV: the names and values of any environment variables
  • $_GET: information submitted as a GET request
  • $_POST: information submitted as a POST request
  • $_COOKIE: names and values of any cookies passed as part of a request
  • $_SERVER: information about the web server
  • $_FILES: information about any uploaded files

Class exercise

• The $_SERVER array contains many keys/values:
  http://ie.php.net/manual/en/reserved.variables.server.php
• One is HTTP_USER_AGENT, which gives the string the browser used to identify itself
• Write a PHP script that tries to detect what browser the user is using ('Firefox', 'MSIE' or other) and outputs some messages of your choosing accordingly
• Pretend that there is a built-in function in_string( $s1, $s2 ), which returns true if string s1 is contained within string s2, and false otherwise (Surprisingly, there isn't such a function that is exactly like this)
• Note this script will not be particularly reliable: browsers keep changing the way they identify themselves; some choose not to identify themselves; some firewalls block the browser identity