C# TrimStart with string parameter

Question

I\'m looking for String extension methods for TrimStart() and TrimEnd() that accept a string parameter.

I could build one myself but I\'m alw

Answer 1

from dotnetperls.com,

Performance

Unfortunately, the TrimStart method is not heavily optimized. In specific situations, you will likely be able to write character-based iteration code that can outperform it. This is because an array must be created to use TrimStart.

However: Custom code would not necessarily require an array. But for quickly-developed applications, the TrimStart method is useful.

Answer 2

To match entire string and not allocate multiple substrings, you should use the following:

    public static string TrimStart(this string source, string value, StringComparison comparisonType)
    {
        if (source == null)
        {
            throw new ArgumentNullException(nameof(source));
        }

        int valueLength = value.Length;
        int startIndex = 0;
        while (source.IndexOf(value, startIndex, comparisonType) == startIndex)
        {
            startIndex += valueLength;
        }

        return source.Substring(startIndex);
    }

    public static string TrimEnd(this string source, string value, StringComparison comparisonType)
    {
        if (source == null)
        {
            throw new ArgumentNullException(nameof(source));
        }

        int sourceLength = source.Length;
        int valueLength = value.Length;
        int count = sourceLength;
        while (source.LastIndexOf(value, count, comparisonType) == count - valueLength)
        {
            count -= valueLength;
        }

        return source.Substring(0, count);
    }

Answer 3

There is no built in function in C# - but you can write your own extension methods which I will show you below - they can be used like the builtin ones to trim characters, but here you can use strings to trim.

Note that with IndexOf / LastIndexOf, you can choose if it is case sensitive / culture sensitive or not.

I have implemented the feature "repetitive trims" as well (see the optional parameters).

Usage:

var trimmed1 = myStr.TrimStart(trimStr); 
var trimmed2 = myStr.TrimEnd(trimStr);
var trimmed3 = myStr.TrimStr(trimStr);
var trimmed4 = myStr.Trim(trimStr);

There is one function TrimStr(..) trimming from the start and from the end of the string, plus three functions implementing .TrimStart(...), .TrimEnd(...) and .Trim(..) for compatibility with the .NET trims:

Try it in DotNetFiddle

public static class Extension
{
    public static string TrimStr(this string str, string trimStr, 
                  bool trimEnd = true, bool repeatTrim = true,
                  StringComparison comparisonType = StringComparison.OrdinalIgnoreCase)
    {
        int strLen;
        do
        {
            if (!(str ?? "").EndsWith(trimStr)) return str;
            strLen = str.Length;
            {
             if (trimEnd)
                {
                  var pos = str.LastIndexOf(trimStr, comparisonType);
                  if ((!(pos >= 0)) || (!(str.Length - trimStr.Length == pos))) break;
                  str = str.Substring(0, pos);
                }
                else
                {
                  var pos = str.IndexOf(trimStr, comparisonType);
                  if (!(pos == 0)) break;
                  str = str.Substring(trimStr.Length, str.Length - trimStr.Length);
                }
            }
        } while (repeatTrim && strLen > str.Length);
        return str;
    }

     // the following is C#6 syntax, if you're not using C#6 yet
     // replace "=> ..." by { return ... }

    public static string TrimEnd(this string str, string trimStr, 
            bool repeatTrim = true,
            StringComparison comparisonType = StringComparison.OrdinalIgnoreCase) 
            => TrimStr(str, trimStr, true, repeatTrim, comparisonType);

    public static string TrimStart(this string str, string trimStr, 
            bool repeatTrim = true,
            StringComparison comparisonType = StringComparison.OrdinalIgnoreCase) 
            => TrimStr(str, trimStr, false, repeatTrim, comparisonType);

    public static string Trim(this string str, string trimStr, bool repeatTrim = true,
        StringComparison comparisonType = StringComparison.OrdinalIgnoreCase) 
        => str.TrimStart(trimStr, repeatTrim, comparisonType)
              .TrimEnd(trimStr, repeatTrim, comparisonType);

}

Now you can just use it like

    Console.WriteLine("Sammy".TrimEnd("my"));
    Console.WriteLine("moinmoin gibts gips? gips gibts moin".TrimStart("moin", false));
    Console.WriteLine("moinmoin gibts gips? gips gibts moin".Trim("moin").Trim());

which creates the output

Sam
moin gibts gips? gips gibts moin
gibts gips? gips gibts