syntax.php

<?php
function highlightText($text) {
    $text = trim($text);
    $text = highlight_string("<?php " . $text, true);  // highlight_string() requires opening PHP tag or otherwise it will not colorize the text
    $text = trim($text);
    $text = preg_replace("|^\\<code\\>\\<span style\\=\"color\\: #[a-fA-F0-9]{0,6}\"\\>|", "", $text, 1);  // remove prefix
    $text = preg_replace("|\\</code\\>\$|", "", $text, 1);  // remove suffix 1
    $text = trim($text);  // remove line breaks
    $text = preg_replace("|\\</span\\>\$|", "", $text, 1);  // remove suffix 2
    $text = trim($text);  // remove line breaks
    $text = preg_replace("|^(\\<span style\\=\"color\\: #[a-fA-F0-9]{0,6}\"\\>)(&lt;\\?php&nbsp;)(.*?)(\\</span\\>)|", "\$1\$3\$4", $text);  // remove custom added "<?php "

    return $text;
}

$code = file_get_contents('c.cpp');
echo highlightText($code);
?>