Question

I wrote the code below to replace strings but it seemed like there is something wrong with the code. It couldn’t replace multiple times. It only can replace the first occurrence. It suppose to replace all occurrences.

//Do not use System.Security.SecurityElement.Escape. I am writing this code for multiple .NET versions.

public string UnescapeXML(string s)
{
    if (string.IsNullOrEmpty(s)) return s;
    return s.Replace("&amp;", "&").Replace("&apos;", "'").Replace("&quot;", "\"").Replace("&gt;", ">").Replace("&lt;", "<");
}

protected void Page_Load(object sender, EventArgs e)
{

    string TestData="TestData&amp;amp;amp;";
    Response.Write("using function====>>>>" + UnescapeXML(TestData));
    Response.Write("\n\n<BR>Not using function====>>>>" + TestData.Replace("&amp;", ""));

}

Answer 1

Your function is operating correctly, assuming you want a one-pass (per substring) solution.

Your testDate is missing & characters before amp;

Change to:

string TestData="TestData&&&";

From:

string TestData="TestData&";

What is a one-pass (per substring) solution?

1. Each unique substring1 occurrence is changed.
2. Then, each unique substring2 occurrence is changed.
3. …
4. Then, each unique substringN occurrence is changed.

Recursive Alternative

A recursive solution would involve the following:

1. After one-single substring replacement, you call the function again

2. If no replacements occured, return the string

   public string ReplaceStuff(string MyStr) {   
     //Attempt to replace 1 substring
   
     if ( ReplacementOccurred ){
       return ReplaceStuff(ModifiedString);
     }else{
       return MyStr;
     } 
   }
   

What do you get with Recursion?

• Well, given an input string: &, it would first be changed to &, then the next level of recursion would change it to &.
• I honestly don’t think the author wants the recursive solution, but I could see how passersby might.