でけた

Perlのようなもの 



do {

	$tmp = <STDIN>;

	$_ .= $tmp;

} while ($tmp);
# & -> &amp;

s/&/&amp;/g;
# < -> &lt;

s/</&lt;/g;
# > -> &gt;

s/>/&gt;/g;
$keywords = "(auto|bool|catch|char|class|const|const_cast|do|double|dynamic_cast|enum|export|extern|float|for|goto|if|inline|int"

	."|long|mutable|namespace|operator|private|protected|ptrdiff_t|public|register|reinterpret_cast|return|signed|size_t|sizeof|short"

	."|static|static_cast|struct|template|this|throw|try|typedef|typeid|typename|union|unsigned|using|virtual|void|volatile|wchar_t|while)";

$string = qq/"(?:[^"\\\\]|\\\\(?:.|\\n))"/;

$char = qq/'(?:[^'\\\\]|\\\\(?:.|\\n))'/;

$comment = qq%//(?:[^\\\\]|\\\\(?:.|\\n))*?\\n|/\\*(?:[^\\\\]|\\\\(?:.|\\n))*?\\*/%;
# keywords

s%((?:[^"'\\/]|\\.|/[^*/]|$comment|$string|$char)*?)\b($keywords)\b%\1<span class="keywords">\2</span>%xg;
# string

s%((?:[^"'<\\/]|\\.|/[^*/]|$comment|$char|<.*?>)*?)($string)%\1<span class="string">\2</span>%xg;
# char

s%((?:[^"'<\\/]|\\.|/[^*/]|$comment|$string|<.*?>)*?)($char)%\1<span class="char">\2</span>%xg;
# comment

s%((?:[^"'<\\/]|\\.|/[^*/]|$string|$char|<.*?>)*?)($comment)%\1<span class="comment">\2</span>%xg;
# <iostream>

s%(\n?[ 	]*)(#[ 	]*include)((?:[^\\<"']|\\.)*?)(&lt;(?:[^\\]|\\.)*?&gt;)%\1\2\3<span class="string">\4</span>%g;
# preprocess

s%(\n?[ 	]*)(#[ 	]*)(ifdef|ifndef|if|elif|else|endif|define|include|error|warning|pragma)\b%\1<span class="preprocess">\2\3</span>%g;
print qq/<pre class="cpp">\n/;

print;

print "</pre>\n";

こんなんでどう？
何時頃かに直上のコードをちょっと変更。相変わらず\の処理は適当。あとtypeid追加。忘れてた。
あと整数・浮動小数リテラルはTodoで。