Chris's coding blog

Syntax highlighter for C#

April 07, 2010

This is small class for color coding, syntax highlighting, pretty printing, prettifying (any of the above) C# source code. It produces HTML with span tags and a css class. It’s not perfect and undoubtedly has bugs in it, but on the whole works. It was written in a lunchhour and given some spit and polish at night - any suggestions or bugs you find are welcomed.

The online demo is no longer available, however there is an even better version at Manoli.net

Here’s an overview:

  • It’s not a beautifully engineered state machine and does not work for any language or geared for re-use. It has some re-useability through limited inheritence but is mostly aimed at one feature: producing HTML source code of prettified C#.
  • If you want a BNF/state machine based syntax highlighter for ASP.NET the free Actipro CodeHighlighter is a good choice, and uses ANTLR for its parsing.
  • Uses 4 CSS classes which you can configure through properties: keyword, comment, type, quote
  • Has an option to insert the default Visual Studio colours as a stylesheet. This is true by default.
  • Has the ability to wrap your source in pre tags
  • Has the ability to add keywords via a string List. Comes with a set of default C# ones (and the list is probably missing some keywords)
  • It could quite easily be modified for Java, C and C++.

Bare in mind it’s not perfect, and can occasionally get confused. On the whole though I’ve found it highlights fairly reliably.

This is how it works. It’s fairly simple: 2 methods, the HighlightSource does the hard work. It does the following:

  1. Removes all /**/ comments, inserts a token placeholder, appended with a number. This is done via a regex from website
  2. Removes all quotes and places token placeholders in their place. This isn’t done with a regex, it probably can be but I found it easier with simple looping through a char array and some basic state flags
  3. Removes all // comments (including XML documentation ones) and puts a token placeholder in their place.
  4. Highlights types. This is done in 4 regex passes, gradually replacing small variations. The basic rule is space, capital, alphanumeric,space with variations for generics and new instances.
  5. Replaces keywords with some basic string.Replace() calls.
  6. Replaces the token placeholders in 1-3 back, with their CSS.

/// <summary>
/// A basic implementation of a pretty-printer or syntax highlighter for C# soure code.
/// </summary>
public class SourceColorer
{
private string _commentCssClass;
private string _keywordCssClass;
private string _quotesCssClass;
private string _typeCssClass;
private bool _addStyleDefinition;
private HashSet<string> _keywords;
private bool _addPreTags;
/// <summary>
/// Gets the list of reserved words/keywords.
/// </summary>
public HashSet<string> Keywords
{
get { return _keywords; }
}
/// <summary>
/// Gets or sets the CSS class used for comments. The default is 'comment'.
/// </summary>
public string CommentCssClass
{
get { return _commentCssClass; }
set { _commentCssClass = value; }
}
/// <summary>
/// Gets or sets the CSS class used for keywords. The default is 'keyword'.
/// </summary>
public string KeywordCssClass
{
get { return _keywordCssClass; }
set { _keywordCssClass = value; }
}
/// <summary>
/// Gets or sets the CSS class used for string quotes. The default is 'quotes'.
/// </summary>
public string QuotesCssClass
{
get { return _quotesCssClass; }
set { _quotesCssClass = value; }
}
/// <summary>
/// Gets or sets the CSS class used for types. The default is 'type'.
/// </summary>
public string TypeCssClass
{
get { return _typeCssClass; }
set { _typeCssClass = value; }
}
/// <summary>
/// Whether to add the CSS style definition to the top of the highlighted code.
/// </summary>
public bool AddStyleDefinition
{
get { return _addStyleDefinition; }
set { _addStyleDefinition = value; }
}
/// <summary>
/// Whether to insert opening and closing pre tags around the highlighted code.
/// </summary>
public bool AddPreTags
{
get { return _addPreTags; }
set { _addPreTags = value; }
}
/// <summary>
/// Initializes a new instance of the <see cref="SourceColorer"/> class.
/// </summary>
public SourceColorer()
{
_addStyleDefinition = true;
_commentCssClass = "comment";
_keywordCssClass = "keyword";
_quotesCssClass = "quotes";
_typeCssClass = "type";
_keywords = new HashSet<string>()
{
"static", "using", "true", "false","new",
"namespace", "void", "private", "public",
"bool", "string", "return", "class","internal",
"const", "readonly", "int", "double","lock",
"float", "if", "else", "foreach", "for","var",
"get","set","byte\\[\\]","char\\[\\]","int\\[\\]","string\\[\\]" // dumb array matching. Escaped as [] is regex syntax
};
}
/// <summary>
/// Highlights the specified source code and returns it as stylised HTML.
/// </summary>
/// <param name="source">The source code.</param>
/// <returns></returns>
public string Highlight(string source)
{
StringBuilder builder = new StringBuilder();
if (AddStyleDefinition)
{
builder.Append("<style>");
builder.AppendFormat(".{0} {{ color: #0000FF }} ", KeywordCssClass);
builder.AppendFormat(".{0} {{ color: #2B91AF }} ", TypeCssClass);
builder.AppendFormat(".{0} {{ color: green }} ", CommentCssClass);
builder.AppendFormat(".{0} {{ color: maroon }} ", QuotesCssClass);
builder.Append("</style>");
}
if (AddPreTags)
builder.Append("<pre>");
builder.Append(HighlightSource(source));
if (AddPreTags)
builder.Append("</pre>");
return builder.ToString();
}
/// <summary>
/// Occurs when the source code is highlighted, after any style (CSS) definitions are added.
/// </summary>
/// <param name="content">The source code content.</param>
/// <returns>The highlighted source code.</returns>
protected virtual string HighlightSource(string content)
{
if (string.IsNullOrEmpty(CommentCssClass))
throw new InvalidOperationException("The CommentCssClass should not be null or empty");
if (string.IsNullOrEmpty(KeywordCssClass))
throw new InvalidOperationException("The KeywordCssClass should not be null or empty");
if (string.IsNullOrEmpty(QuotesCssClass))
throw new InvalidOperationException("The CommentCssClass should not be null or empty");
if (string.IsNullOrEmpty(TypeCssClass))
throw new InvalidOperationException("The TypeCssClass should not be null or empty");
// Some fairly secure token placeholders
const string COMMENTS_TOKEN = "`````";
const string MULTILINECOMMENTS_TOKEN = "~~~~~";
const string QUOTES_TOKEN = "¬¬¬¬¬";
// Remove /* */ quotes, taken from ostermiller.org
Regex regex = new Regex(@"/\*([^*]|[\r\n]|(\*+([^*/]|[\r\n])))*\*+/", RegexOptions.Singleline);
List<string> multiLineComments = new List<string>();
if (regex.IsMatch(content))
{
foreach (Match item in regex.Matches(content))
{
if (!multiLineComments.Contains(item.Value))
multiLineComments.Add(item.Value);
}
}
for (int i = 0; i < multiLineComments.Count; i++)
{
content = content.ReplaceToken(multiLineComments[i], MULTILINECOMMENTS_TOKEN, i);
}
// Remove the quotes first, so they don't get highlighted
List<string> quotes = new List<string>();
bool onEscape = false;
bool onComment1 = false;
bool onComment2 = false;
bool inQuotes = false;
int start = -1;
for (int i = 0; i < content.Length; i++)
{
if (content[i] == '/' && !inQuotes && !onComment1)
onComment1 = true;
else if (content[i] == '/' && !inQuotes && onComment1)
onComment2 = true;
else if (content[i] == '"' && !onEscape && !onComment2)
{
inQuotes = true; // stops cases of: var s = "// I'm a comment";
if (start > -1)
{
string quote = content.Substring(start, i - start + 1);
if (!quotes.Contains(quote))
quotes.Add(quote);
start = -1;
inQuotes = false;
}
else
{
start = i;
}
}
else if (content[i] == '\\' || content[i] == '\'')
onEscape = true;
else if (content[i] == '\n')
{
onComment1 = false;
onComment2 = false;
}
else
{
onEscape = false;
}
}
for (int i = 0; i < quotes.Count; i++)
{
content = content.ReplaceToken(quotes[i], QUOTES_TOKEN, i);
}
// Remove the comments next, so they don't get highlighted
regex = new Regex("(/{2,3}.+)\n", RegexOptions.Multiline);
List<string> comments = new List<string>();
if (regex.IsMatch(content))
{
foreach (Match item in regex.Matches(content))
{
if (!comments.Contains(item.Value + "\n"))
comments.Add(item.Value);
}
}
for (int i = 0; i < comments.Count; i++)
{
content = content.ReplaceToken(comments[i], COMMENTS_TOKEN, i);
}
// Highlight single quotes
content = Regex.Replace(content, "('.{1,2}')", "<span class=\"quote\">$1</span>", RegexOptions.Singleline);
// Highlight class names based on the logic: {space OR start of line OR >}{1 capital){alphanumeric}{space}
regex = new Regex(@"((?:\s|^)[A-Z]\w+(?:\s))", RegexOptions.Singleline);
List<string> highlightedClasses = new List<string>();
if (regex.IsMatch(content))
{
foreach (Match item in regex.Matches(content))
{
string val = item.Groups[1].Value;
if (!highlightedClasses.Contains(val))
highlightedClasses.Add(val);
}
}
for (int i = 0; i < highlightedClasses.Count; i++)
{
content = content.ReplaceWithCss(highlightedClasses[i], TypeCssClass);
}
// Pass 2. Doing it in N passes due to my inferior regex knowledge of back/forwardtracking.
// This does {space or [}{1 capital){alphanumeric}{]}
regex = new Regex(@"(?:\s|\[)([A-Z]\w+)(?:\])", RegexOptions.Singleline);
highlightedClasses = new List<string>();
if (regex.IsMatch(content))
{
foreach (Match item in regex.Matches(content))
{
string val = item.Groups[1].Value;
if (!highlightedClasses.Contains(val))
highlightedClasses.Add(val);
}
}
for (int i = 0; i < highlightedClasses.Count; i++)
{
content = content.ReplaceWithCss(highlightedClasses[i], TypeCssClass);
}
// Pass 3. Generics
regex = new Regex(@"(?:\s|\[|\()([A-Z]\w+(?:<|&lt;))", RegexOptions.Singleline);
highlightedClasses = new List<string>();
if (regex.IsMatch(content))
{
foreach (Match item in regex.Matches(content))
{
string val = item.Groups[1].Value;
if (!highlightedClasses.Contains(val))
highlightedClasses.Add(val);
}
}
for (int i = 0; i < highlightedClasses.Count; i++)
{
string val = highlightedClasses[i];
val = val.Replace("<", "").Replace("&lt;", "");
content = content.ReplaceWithCss(highlightedClasses[i], val, "&lt;", TypeCssClass);
}
// Pass 4. new keyword with a type
regex = new Regex(@"new\s+([A-Z]\w+)(?:\()", RegexOptions.Singleline);
highlightedClasses = new List<string>();
if (regex.IsMatch(content))
{
foreach (Match item in regex.Matches(content))
{
string val = item.Groups[1].Value;
if (!highlightedClasses.Contains(val))
highlightedClasses.Add(val);
}
}
// Replace the highlighted classes
for (int i = 0; i < highlightedClasses.Count; i++)
{
content = content.ReplaceWithCss(highlightedClasses[i], TypeCssClass);
}
// Highlight keywords
foreach (string keyword in _keywords)
{
Regex regexKeyword = new Regex("(" + keyword + @")(>|&gt;|\s|\n|;|<)", RegexOptions.Singleline);
content = regexKeyword.Replace(content, "<span class=\"keyword\">$1</span>$2");
}
// Shove the multiline comments back in
for (int i = 0; i < multiLineComments.Count; i++)
{
content = content.ReplaceTokenWithCss(multiLineComments[i], MULTILINECOMMENTS_TOKEN, i, CommentCssClass);
}
// Shove the quotes back in
for (int i = 0; i < quotes.Count; i++)
{
content = content.ReplaceTokenWithCss(quotes[i], QUOTES_TOKEN, i, QuotesCssClass);
}
// Shove the single line comments back in
for (int i = 0; i < comments.Count; i++)
{
string comment = comments[i];
// Add quotes back in
for (int n = 0; n < quotes.Count; n++)
{
comment = comment.Replace(string.Format("{0}{1}{0}", QUOTES_TOKEN, n), quotes[n]);
}
content = content.ReplaceTokenWithCss(comment, COMMENTS_TOKEN, i, CommentCssClass);
}
return content;
}
}
public static class MoreExtensions
{
public static string ReplaceWithCss(this string content, string source, string cssClass)
{
return content.Replace(source, string.Format("<span class=\"{0}\">{1}</span>", cssClass, source));
}
public static string ReplaceWithCss(this string content, string source, string replacement, string cssClass)
{
return content.Replace(source, string.Format("<span class=\"{0}\">{1}</span>", cssClass, replacement));
}
public static string ReplaceWithCss(this string content, string source, string replacement, string suffix, string cssClass)
{
return content.Replace(source, string.Format("<span class=\"{0}\">{1}</span>{2}", cssClass, replacement, suffix));
}
public static string ReplaceTokenWithCss(this string content, string source, string token, int counter, string cssClass)
{
string formattedToken = String.Format("{0}{1}{0}", token, counter);
return content.Replace(formattedToken, string.Format("<span class=\"{0}\">{1}</span>", cssClass, source));
}
public static string ReplaceToken(this string content, string source, string token, int counter)
{
string formattedToken = String.Format("{0}{1}{0}", token, counter);
return content.Replace(source, formattedToken);
}
}
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Chris Small

I'm Chris Small, a software engineer living and working in London. This is my tech blog. Find out more via GithubStackoverflowResume