Class CodeBlock (heeft CSS nodig):
[code=php]<?php
/*
 * Class for printing code in a HTML formatted block, complete with line numbers.
 * It is also suited to be included in other UBB-like functionality.
 */
class CodeBlock
{
    protected $options;
    protected $output;

    public function __construct($text, $options=array()) {
        // Set options; first overwrites second (the defaults).
        $this->options = $options + self::getDefaultOptions();

        // Do we still need to strip tags?
        if (!$this->options['tags_stripped'] && ini_get('magic_quotes_gpc')) {
            $returnText = stripslashes($text);
        } else {
            $returnText = $text;
        }

        // Convert any tabs to spaces.
        $returnText = str_replace("\t", str_repeat(' ', $this->options['tabspaces']), $returnText);

        // Convert all linebreaks to "\n".
        $returnText = str_replace("\r\n", "\n", $returnText);

        // Remove all whitespace characters from the end of each line, this will also trim empty lines.
        $lines      = explode("\n", $returnText);
        $returnText = implode("\n", array_map('rtrim', $lines));

        // Do we want to apply PHP code highlighting?
        if ($this->options['highlight']) {
            $returnText = @highlight_string($returnText, true); // suppress possible errors

            // Clean up some of the HTML generated by highlight_string():
            // Replace all <br /> tags with "\n" and fix the start and end of the returned HTML.
            $returnText = str_replace(
                array('<br />', '<code><span style="color: #000000">'."\n", '</span>'."\n".'</code>'),
                array("\n",     '<span style="color: #000000">',            '</span>'),
                $returnText
            );
        } else {
            // Just neutralize everything.
            $returnText = htmlspecialchars($returnText, ENT_QUOTES, 'UTF-8');
        }

        // Create the code block, starting with linenumbers.
        $nrs = implode("\n", range(1, count($lines))); // seems faster than a for-loop, alternatively: use <br /> instead of \n for implosion
        ob_start();
            ?><div class="code-wrapper">
                <div class="index"><pre><?php echo $nrs ?></pre></div>
                <div class="code"><pre><?php echo $returnText ?></pre></div>
            </div><?php
        $this->output = ob_get_clean();
    } // __construct

    public static function getDefaultOptions() {
        return array(
            'tabspaces'     => 4,       // number of spaces that tab-characters are replaced with
            'highlight'     => true,    // whether to use the PHP function highlight_string() for highlighting code
            // The next default should not be changed here unless you use the CodeBlock class directly,
            // or when magic_quotes_gpc is on but you already stripped these extra slashes before you
            // passed the input to this class.
            'tags_stripped' => false,   // keeps track of whether we already stripped tags for when magic_quotes_gpc is on
        );
    } // getDefaultOptions

    public function getOutput() {
        return $this->output;
    } // getOutput
} // class
?>

Bijbehorende CSS:
[code=css]@CHARSET "UTF-8";

div.code-wrapper            { display: block; margin: 0; padding: 0; border: 1px solid #cccccc; background-color: #eeeeee; position: relative; overflow-x: auto; overflow-y: hidden; }
div.code-wrapper pre        { font-family: monospace; font-size: 13px; margin: 0; padding: 2px 5px; border: 0; line-height: 15px; }
div.code-wrapper div        { margin: 0; padding: 0; border: 0; }
div.code-wrapper div.index  { display: block; width: 40px; text-align: right; background-color: #cccccc; color: #333333; }
div.code-wrapper div.code   { display: block; position: absolute; top: 0px; left: 40px; color: #000000; }

Class Ubb:
[code=php]<?php
/*
 * Class for formatting output, codeblocks can be picked up as well.
 */
class Ubb
{
    protected $options;
    protected $output;
    protected $codeBlocks;  // stack (array) of CodeBlock objects
    protected $tag;         // shorthand for $this->options['code_block_tag'], used for delimiting blocks of code

    public function __construct($text, $options=array()) {
        $this->codeBlocks = array();

        $this->options = $options + array(
            'allow_html'            => false,   // allow HTML outside code blocks? be VERY careful with this
            'use_code_block'        => true,    // use CodeBlock class for formatting blocks of code?
            'code_block_tag'        => 'code',  // name of the UBB-tag for delimiting blocks of code, it will also enable us to print this code using this class :)
            'code_block_options'    => array(), // styling options for code blocks, see CodeBlock::getDefaultOptions()
        );
        $this->options['code_block_options'] = $this->options['code_block_options'] + CodeBlock::getDefaultOptions();

        $this->tag = $this->options['code_block_tag'];

        // Strip slashes if magic_quotes_gpc is on.
        if (ini_get('magic_quotes_gpc')) {
            $returnText = stripslashes($text);
        } else {
            $returnText = $text;
        }
        // We stripped tags; do not strip them again in CodeBlock calls.
        $this->options['code_block_options']['tags_stripped'] = true;

        if ($this->options['use_code_block']) {
            // Backup code blocks, it needs separate treatment from the rest of the UBB-code).
            // preg_replace() will become deprecated in PHP 5.5.0, we use preg_replace_callback instead.
            $returnText = preg_replace_callback(
                '#\['.$this->tag.'](.*)\[/'.$this->tag.']#sU',
                array($this, 'backupCodeBlock'),
                $returnText
            );
        }

        // Perform the rest of the UBB formatting, starting with (dis)allowing HTML.
        if ($this->options['allow_html'] == false) {
            // No HTML allowed, neutralize all HTML and convert newline characters to linebreak-tags.
            $returnText = nl2br(htmlspecialchars($returnText, ENT_QUOTES, 'UTF-8'));

            if ($this->options['use_code_block']) {
                // Some extra styling: remove the <br /> after the closing tag of a code block.
                $returnText = str_replace('[/'.$this->tag.']<br />', '[/'.$this->tag.']', $returnText);
            }
        } // allow_html false

        // Put the rest, if any, of your own UBB-styling here.

        if ($this->options['use_code_block']) {
            // Restore code blocks.
            $returnText = preg_replace_callback(
                '#\['.$this->tag.'](\d+)\[/'.$this->tag.']#sU',
                array($this, 'restoreCodeBlock'),
                $returnText
            );
        }

        // Store the processed input in $this->output.
        $this->output = $returnText;
    } // __construct

    // Callback function for storing blocks of code.
    protected function backupCodeBlock($matches) {
        $currentBlock = count($this->codeBlocks);

        $this->codeBlocks[$currentBlock] = new CodeBlock(
            // Note: strip backslash from escaped double quotes due to /e-switch is no longer necessary
            //       because we do not use preg_match anymore.
            $matches[1],
            $this->options['code_block_options']
        );

        // Return a HTML-safe placeholder to indicate where the codeblock should be placed back after
        // processing the rest of the UBB-code.
        return '['.$this->tag.']'.$currentBlock.'[/'.$this->tag.']';
    } // backupCodeBlock

    // Callback function for restoring code blocks after the rest of the UBB-code is applied.
    protected function restoreCodeBlock($matches) {
        return $this->codeBlocks[$matches[1]]->getOutput();
    } // restoreCodeBlock

    public function getOutput() {
        return $this->output;
    }
} // class
?>

Gebruik:
Voor het afdrukken van één groot codeblock:
[code=php]<?php
// creeer een CodeBlock object
$code = new CodeBlock('je_code_hier');

// afdrukken!
echo $code->getOutput();
?>

Voor het adrukken van een UBB-tekst met hierin codeblokken:
[code=php]<?php
// creeer een Ubb object
$ubb = new Ubb('je_tekst_met_codeblokken_hier');

// afdrukken!
echo $ubb->getOutput();
?>

Je kunt ook een aantal opties meegeven (in zowel CodeBlock als Ubb), bijvoorbeeld je staat HTML toe (buiten codeblokken), je wilt geen highlight_string gebruiken voor PHP-code:
[code=php]<?php
// aanmaken en instellen
$ubb = new Ubb('je_tekst_met_codeblokken_hier', array(
    'allow_html' => true,
    'code_block_options' => array(
        'highlight' => false,
    ),
));

// afdrukken
echo $ubb->getOutput();
?>