CODEWITHSUNDEEP
c#string
Ian Kremer
Ian Kremer

Reputation: 379

Replace & with & in C#

Ok I feel really stupid asking this. I see plenty of other questions that resemble my question, but none seem to be able to answer it.

I am creating an xml file for a program that is very picky about syntax. Sadly I am making the XML file from scratch. Meaning, I am placing each line in individually (lots of file.WriteLine(String)).

I know this is ugly, but its the only way I can get the logic to work out.

ANYWAY. I have a few strings that are coming through with '&' in them.

if (value.Contains("&"))
   {
      value.Replace("&", "&");
   }

Does not seem to work. The value.Contains() seems to see it, but the replace does not work. I am using C# .Net 2.0 sp2. VS 2005.

Please help me out here.. Its been a long week..

Upvotes: 12

Views: 55443

Answers (13)

nimblebit
nimblebit

Reputation: 559

There is a potential problem with just doing the following

input.Replace("&", "&");

If your source text has partially escaped characters and some unescaped characters (from user error), when the input.Replace function is applied your output will have escape applied again on a character that has already been handled.

Issue

Before: "My Sample Text"
On input.Replace the text will become "My Sample Text"

To avoid this, if your source text already has some escaped characters do the following before applying the ampersand replace

  1. Unescape the existing text
  2. Escape the new text - to apply the ampersand formatting

Example 1

using System;
using System.Text;
                    
public class Program
{
    private const string CHARACTER_AMPERSAND = "&";
    private const string CHARACTER_SPACE = " ";
    private const string CHARACTER_APOSTROPHE = "'";
    private const string CHARACTER_QUOTE = """;
    private const string CHARACTER_LESS_THAN = "<";
    private const string CHARACTER_GREATER_THAN = ">";
        
    public static void Main()
    {
        var sb = new StringBuilder("Text with partially escaped characters & "01234567890"");
        
        Console.WriteLine("1. Start Text: " + sb.ToString());
        
        UnescapeCharacters(sb);
        
        Console.WriteLine("2. Unescape the existing text: " + sb.ToString());
        
        EscapeCharacters(sb);
        
        Console.WriteLine("3. Escape the new text - Apply the ampersand formatting: " + sb.ToString());
    }
    
    // unescape special characters
    private static void UnescapeCharacters(StringBuilder sb)
    {
        sb.Replace(CHARACTER_AMPERSAND, "&") // remove special characters
          .Replace(CHARACTER_SPACE, " ")
          .Replace(CHARACTER_APOSTROPHE, "'")
          .Replace(CHARACTER_QUOTE, "\"")
          .Replace(CHARACTER_LESS_THAN, "<")
          .Replace(CHARACTER_GREATER_THAN, ">");
    }
    
    // escape special characters suitable for xml
    private static void EscapeCharacters(StringBuilder sb)
    {
        sb.Replace("&", CHARACTER_AMPERSAND)
          .Replace("'", CHARACTER_APOSTROPHE)
          .Replace("\"", CHARACTER_QUOTE)
          .Replace("<", CHARACTER_LESS_THAN)
          .Replace(">", CHARACTER_GREATER_THAN);
    }
    
}

This sample will generate the following output

1. Start Text: Text with partially escaped characters & &quot;01234567890&quot;
2. Unescape the existing text: Text with partially escaped characters & "01234567890"
3. Escape the new text - Apply the ampersand formatting: Text with partially escaped characters &amp; &quot;01234567890&quot;

Example 2 - Recursion (not as good as the first example)

using System;
using System.Text;
using System.Linq;
                    
public class Program
{
    private const string CHARACTER_AMPERSAND = "&amp;";
    private const string CHARACTER_SPACE = "&nbsp;";
    private const string CHARACTER_APOSTROPHE = "&apos;";
    private const string CHARACTER_QUOTE = "&quot;";
    private const string CHARACTER_LESS_THAN = "&lt;";
    private const string CHARACTER_GREATER_THAN = "&gt;";
        
    public static void Main()
    {
        var sb = new StringBuilder("Text with partially escaped characters & &quot;01234567890&quot; (A&B)");
                
        Console.WriteLine("Start Text: " + sb.ToString());
        
        UnescapeCharacters(sb);
        
        Console.WriteLine("Unescaped Text: " + sb.ToString());
        
        var splitText = sb.ToString().Split(' '); // split words by space character
        
        var wordsContainingAmpersand = splitText.Where(i => i.Contains("&"));
        
        if (wordsContainingAmpersand.Any())
        {
            foreach (var item in wordsContainingAmpersand)
            {
                Console.WriteLine("Matched word: " + item);

                if (item.Length == 1)
                {
                    Console.WriteLine("Change from: [" + item + " ] to [" + CHARACTER_AMPERSAND + " ]");
                    sb.Replace(item + " ", CHARACTER_AMPERSAND + " ");
                }
                else
                {
                    Console.WriteLine("Change from: [" + item + "] to [" + item.Replace("&", CHARACTER_AMPERSAND) + "]");
                    sb.Replace(item, item.Replace("&", CHARACTER_AMPERSAND));
                }
            }
            
            Console.WriteLine("Fixed Text: " + sb.ToString());
            
            EscapeCharacters(sb);
            
            Console.WriteLine("Escaped Text: " + sb.ToString());
        }
        else
        {
            Console.WriteLine("No matching");
        }
            
    }
    
    private static void EscapeCharacters(StringBuilder sb)
    {
        // ampersand excluded because this is handled within the recursion
        sb.Replace("'", CHARACTER_APOSTROPHE)
          .Replace("\"", CHARACTER_QUOTE)
          .Replace("<", CHARACTER_LESS_THAN)
          .Replace(">", CHARACTER_GREATER_THAN);
    }
    
    // escape special characters suitable for xml
    private static void UnescapeCharacters(StringBuilder sb)
    {
        sb.Replace(CHARACTER_SPACE, " ") // remove special characters
          .Replace(CHARACTER_APOSTROPHE, "'")
          .Replace(CHARACTER_QUOTE, "\"")
          .Replace(CHARACTER_LESS_THAN, "<")
          .Replace(CHARACTER_GREATER_THAN, ">")
          .Replace(CHARACTER_AMPERSAND, "&");
    }
    
}

This example will generate the following output...

 1. Start Text: Text with partially escaped characters &
    &quot;01234567890&quot; (A&B)
 2. Unescaped Text: Text with partially escaped characters &
    "01234567890" (A&B)
 3. Matched word: &
 4. Change from: [& ] to [&amp; ]
 5. Matched word: (A&B)
 6. Change from: [(A&B)] to [(A&amp;B)]
 7. Fixed Text: Text with partially escaped characters &amp;
    "01234567890" (A&amp;B)
 8. Escaped Text: Text with partially escaped characters &amp;
    &quot;01234567890&quot; (A&amp;B)

Upvotes: 0

Trygve
Trygve

Reputation: 2521

Very late here, but I want to share my solution which handles the cases where you have both & (incorrect xml) and & (valid xml) in the document in addition to other xml character entities.

This solution is only meant for cases where you cannot control generation of the xml, usually because it comes from some external source. If you control the xml generation please use XmlTextWriter as suggested by @Justin Niessner

It is also quite fast and handles all the different xml character entities/references

Predefined character entities:

& quot;

& amp;

& apos;

& lt;

& gt;

Numeric character entities/references:

& #nnnn;

& #xhhhh;

PS! The space after & should not be included in the entities/references, I just added it here to avoid it being encoded in the page rendering

Code

    public static string CleanXml(string text)
    {
        int length = text.Length;
        StringBuilder stringBuilder = new StringBuilder(length);

        for (int i = 0; i < length; ++i)
        {
            if (text[i] == '&')
            {
                var remaining = Math.Abs(length - i + 1);
                var subStrLength = Math.Min(remaining, 12);
                var subStr = text.Substring(i, subStrLength);
                var firstIndexOfSemiColon = subStr.IndexOf(';');
                if (firstIndexOfSemiColon > -1)
                    subStr = subStr.Substring(0, firstIndexOfSemiColon + 1);
                var matches = Regex.Matches(subStr, "&(?!quot;|apos;|amp;|lt;|gt;|#x?.*?;)|'");
                if (matches.Count > 0)
                    stringBuilder.Append("&amp;");
                else
                    stringBuilder.Append("&");
            }
            else if (XmlConvert.IsXmlChar(text[i]))
            {
                stringBuilder.Append(text[i]);
            }
            else if (i + 1 < length && XmlConvert.IsXmlSurrogatePair(text[i + 1], text[i]))
            {
                stringBuilder.Append(text[i]);
                stringBuilder.Append(text[i + 1]);
                ++i;
            }
        }

        return stringBuilder.ToString();
    }

Upvotes: 0

Michael Tobisch
Michael Tobisch

Reputation: 1098

I am quite sure it will work if you "embrace" your value with CDATA, so the result is something like

<ampersandData><![CDATA[value with ampersands like &hellip;]]></ampersandData>

Hope it helps.
Michael

Upvotes: 0

Gonza Oviedo
Gonza Oviedo

Reputation: 1360

I'm Obviously very late to this, but the right answer is:

System.Text.RegularExpressions.Regex.Replace(input, "&(?!amp;)", "&amp;");

Hope this helps somebody!

Upvotes: 5

Jonathan Roberts
Jonathan Roberts

Reputation: 43

What about 

Value = Server.HtmlEncode(Value);

Upvotes: 0

Richard Dufour
Richard Dufour

Reputation: 71

not sure if this is useful to anyone... I was fighting this for a while... here is a glorious regex you can use to fix all your links, javascript, content. I had to deal with a ton of legacy content that nobody wanted to correct.

Add this to your Render override in your master page, control or recode to run a string through it. Please don't flame me for putting this in the wrong place:

// remove the & from href="blaw?a=b&b=c" and replace with &amp; 
//in urls - this corrects any unencoded & not just those in URL's
// this match will also ignore any matches it finds within <script> blocks AND
// it will also ignore the matches where the link includes a javascript command like
// <a href="javascript:alert{'& & &'}">blaw</a>
html = Regex.Replace(html, "&(?!(?<=(?<outerquote>[\"'])javascript:(?>(?!\\k<outerquote>|[>]).)*)\\k<outerquote>?)(?!(?:[a-zA-Z][a-zA-Z0-9]*|#\\d+);)(?!(?>(?:(?!<script|\\/script>).)*)\\/script>)", "&amp;", RegexOptions.Singleline | RegexOptions.IgnoreCase);

Its a broad stroke for a rendered page but this can be adapted to many uses without blowing up your page.

Upvotes: 0

Amitabh
Amitabh

Reputation: 21

I've created the following function to encode & and ' without messing up with already encoded & or ' or "

    public static string encodeSelectXMLCharacters(string xmlString)
    {
        string returnValue = Regex.Replace(xmlString, "&(?!quot;|apos;|amp;|lt;|gt;#x?.*?;)|'",
            delegate(Match m)
            {
                string encodedValue;
                switch (m.Value)
                {
                    case "&":
                        encodedValue = "&amp;";
                        break;
                    case "'":
                        encodedValue = "&apos;";
                        break;
                    default:
                        encodedValue = m.Value;
                        break;
                }

                return encodedValue;
            });
        return returnValue;
    }

Upvotes: 1

mio
mio

Reputation: 31

You can use Regex for replace char "&" only in node values:

input data example (string)

<select>
 <option id="11">Gigamaster&Minimaster</option>
 <option id="12">Black & White</option>
 <option id="13">Other</option>
</select>

Replace with Regex

 Regex rgx = new Regex(">(?<prefix>.*)&(?<sufix>.*)<");
 data = rgx.Replace(data, ">${prefix}&amp;${sufix}<");

 XmlDocument xmlDoc = new XmlDocument();
 xmlDoc.LoadXml(data);

result data

<select>
 <option id="11">Gigamaster&amp;MiniMaster</option>
 <option id="12">Black &amp; White</option>
 <option id="13">Other</option>
</select>

Upvotes: 3

Jim Mischel
Jim Mischel

Reputation: 133975

Strings are immutable. You need to write:

value = value.Replace("&", "&amp;");

Note that if you do this and your string contains "&amp;", it's going to get changed to "&amp;amp;".

Upvotes: 1

Lasse Espeholt
Lasse Espeholt

Reputation: 17782

You should really use something like Linq to XML (XDocument etc.) to solve it. I'm 100% sure you can do it without all your WriteLine´s ;) Show us your logic?

Otherwise you could use this which will be bullet proof (as opposed to .Replace("&")):

var value = "hej&hej<some>";
value = new System.Xml.Linq.XText(value).ToString(); //hej&amp;hej&lt;some&gt;

This will also take care of < which you also HAVE TO escape :)

Update: I have looked at the code for XText.ToString() and internally it creates a XmlWriter + StringWriter and uses XNode.WriteTo. This may be overkill for a given application so if many strings should be converted, XText.WriteTo would be better. An alternative which should be fast and reliant is System.Web.HttpUtility.HtmlEncode.

Update 2: I found this System.Security.SecurityElement.Escape(xml) which may be the fastest and ensures max compatibility (supported since .Net 1.0 and does not require the System.Web reference).

Upvotes: 10

Justin Niessner
Justin Niessner

Reputation: 245399

If you really want to go that route, you have to assign the result of Replace (the method returns a new string because strings are immutable) back to the variable:

value = value.Replace("&", "&amp;");

I would suggest rethinking the way you're writing your XML though. If you switch to using the XmlTextWriter, it will handle all of the encoding for you (not only the ampersand, but all of the other characters that need encoded as well):

using(var writer = new XmlTextWriter(@"C:\MyXmlFile.xml", null))
{
    writer.WriteStartElement("someString");
    writer.WriteText("This is < a > string & everything will get encoded");
    writer.WriteEndElement();
}

Should produce:

<someString>This is &lt; a &gt; string &amp; 
    everything will get encoded</someString>

Upvotes: 39

aslı
aslı

Reputation: 8914

you can also use HttpUtility.HtmlEncode class under System.Web namespace instead of doing the replacement yourself. here you go: http://msdn.microsoft.com/en-us/library/73z22y6h.aspx

Upvotes: 3

Pablo Santa Cruz
Pablo Santa Cruz

Reputation: 181280

You can try:

value = value.Replace("&", "&amp;");

Upvotes: 1

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