I need a case-insensitive Replace method that works with the StringBuilder class

Question

I need a case-insensitive Replace method for the StringBuilder class. The code should work with the existing StringBuilder. An extension method implementation would be nice.

Following is how I plan to use the method:

    [TestMethod]
    public void StringBuilder_Replace_TTD() {

        StringBuilder oRequestText = new StringBuilder(File.ReadAllText("Customer.xml"));

        Customer oCustomer = new Customer(null);

        foreach (FieldIndex iField in Enum.GetValues(typeof(FieldIndex))) {

            oRequestText.Replace("{" iField.ToString() + "}", oCustomer[iField]);

        }

        Debug.WriteLine(oRequestText.ToString());
    }

Answer 1

From: http://blogs.msdn.com/b/btine/archive/2005/03/22/400667.aspx

string Replace( string expr, string find, string repl, bool bIgnoreCase )  
{
// Get input string length
       int exprLen = expr.Length;
       int findLen = find.Length;

       // Check inputs    
       if( 0 == exprLen || 0 == findLen || findLen > exprLen )    
              return expr;

       // Use the original method if the case is required    
       if( !bIgnoreCase )
              return expr.Replace( find, repl );

       StringBuilder sbRet = new StringBuilder( exprLen );

       int pos = 0;              
       while( pos + findLen <= exprLen )    
       {    
              if( 0 == string.Compare( expr, pos, find, 0, findLen, bIgnoreCase ) )    
              {    
                     // Add the replaced string    
                     sbRet.Append( repl );    
                     pos += findLen;    
                     continue;    
              }

              // Advance one character    
              sbRet.Append( expr, pos++, 1 );    
       }

       // Append remaining characters    
       sbRet.Append( expr, pos, exprLen-pos );

       // Return string    
       return sbRet.ToString();    
}

Answer 2

StringBuilder doesn't support using an IComparer when search/replacing text (in fact, there is no search support at all). You could try rolling a character-by-character version, but that will be complicated and may still perform poorly.

Based on your use case, I would suggest using a string rather than StringBuilder, and using string.IndexOf() to locate the positions in the input string where you are going to do replacement - which support case insensitive search. Once you've located all of the replacement regions, create a StringBuilder and then copy each region - replacing found text with the desired replacement values.

EDIT: Presumably you are looking to use replacement with a StringBuilder to avoid allocating additional strings and incurring the performance hit for doing so. However, replacing text within the buffer of a StringBuilder could actually be more expensive - particularly if the replacement strings are of different length than the source string they are replacing. Each replacement requires that characters be shifted forward or backwards depending on whether the replacing text is shorter or longer. Performing memory block moves like this will be expensive.

Answer 3

In your example you want to do (in pseudo code):

StringBuilder oRequestText = ...;
For all fields do replace on oRequestText;
Debug.WriteLine(oRequestText.ToString());

Since you're not actually using the StringBuilder after this there is no functional difference with

StringBuilder oRequestText = ...;
string strRequest = oRequestText.ToString();
For all fields do replace on strRequest;
Debug.WriteLine(strRequest);

The normal replace functions for strings should easily support what you want to do.

I'm assuming in your real situation you do want to use the StringBuilder again. But it's probably still easiest to do a .ToString(), replace on the string, and then reload the StringBuilder with the string.