C# Remove special characters

Question

I want to remove all special characters from a string. Allowed characters are A-Z (uppercase or lowercase), numbers (0-9), underscore (_), white space ( ), pecentage(%) or the dot sign (.).

I have tried this:

        StringBuilder sb = new StringBuilder();
        foreach (char c in input)
        {
            if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') | c == '.' || c == '_' || c == ' ' || c == '%')
            { sb.Append(c); }
        }
        return sb.ToString();

And this:

        Regex r = new Regex("(?:[^a-z0-9% ]|(?<=['\"])s)", RegexOptions.IgnoreCase | RegexOptions.CultureInvariant | RegexOptions.Compiled); 
        return r.Replace(input, String.Empty);

But nothing seems to be working. Any help will be appreciated.

Thank you!

Thank you so much for all the responses. All of them worked for me. I just realized that I forgot to re-publish and that was causing the issue that it was elmenating the white spaces too. — OBL, Apr 15 '11 at 18:50
@Aasmund Eldhuset -- that's freaking funny. At least I wasn't rude about it! :) — Matt Dawdy, Apr 17 '11 at 02:56
Have you looked at [this](http://stackoverflow.com/questions/1120198/most-efficient-way-to-remove-special-characters-from-string) thread on StackOverflow? This guy has a working implementation that you seem to want. — Tejs, Apr 15 '11 at 18:19

score 45 · Answer 1 · answered Apr 15 '11 at 18:26

45

Regex.Replace(input, "[^a-zA-Z0-9% ._]", string.Empty)

answered Apr 15 '11 at 18:26

Sanjeevakumar Hiremath

10,985
3
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46

10

This really is the easiest and most appropriate solution. – Jim Mischel Apr 15 '11 at 20:44

score 16 · Accepted Answer · answered Apr 15 '11 at 18:22

16

You can simplify the first method to

StringBuilder sb = new StringBuilder();
foreach (char c in input)
{
    if (Char.IsLetterOrDigit(c) || c == '.' || c == '_' || c == ' ' || c == '%')
    { sb.Append(c); }
}
return sb.ToString();

which seems to pass simple tests. You can shorten it using LINQ

return new string(
    input.Where(
        c => Char.IsLetterOrDigit(c) || 
            c == '.' || c == '_' || c == ' ' || c == '%')
    .ToArray());

answered Apr 15 '11 at 18:22

Yuriy Faktorovich

67,283
14
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142

11

Be careful with `Char.IsLetterOrDigit`, since it considers *all* Unicode letters and digits. So `Char.IsLetterOrDigit('Ѝ')` returns `true`, because that's a letter in the Cyrillic alphabet. – Jim Mischel Apr 15 '11 at 20:38

score 6 · Answer 3 · answered Apr 15 '11 at 18:18

6

The first approach seems correct, except that you have a | (bitwise OR) instead of a || before c == '.'.

By the way, you should state what doesn't work (doesn't it compile, or does it crash, or does it produce wrong output?)

answered Apr 15 '11 at 18:18

Aasmund Eldhuset

37,289
4
68
81

score 3 · Answer 4 · answered Apr 15 '11 at 18:22

3

StringBuilder sb = new StringBuilder();
foreach (char c in input)
{
    if (char.IsLetterOrDigit(c) || "_ %.".Contains(c.ToString()))
        sb.Append(c);
}
return sb.ToString();

answered Apr 15 '11 at 18:22

Jim Bolla

8,265
36
54

score 1 · Answer 5 · edited Aug 16 '12 at 15:36

1

private string RemoveReservedCharacters(string strValue)
{
    char[] ReservedChars = {'/', ':','*','?','"', '<', '>', '|'};

    foreach (char strChar in ReservedChars)
    {
        strValue = strValue.Replace(strChar.ToString(), "");
    }
    return strValue;
}

edited Aug 16 '12 at 15:36

Jake1164

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6
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64

answered Aug 15 '12 at 22:50

VicSinfuente

11
1

Acceptable solution because of its simplicity. Performance is not that great, because it creates a new string for each replaced character. Why are the ReservedChars not a string[]? Then you wouldn't need to call ToString each time. – Stefan Steinegger Oct 02 '12 at 09:38

score 1 · Answer 6 · answered Apr 15 '11 at 18:22

1

This is how my version might look.

StringBuilder sb = new StringBuilder();
foreach (char c in input)
{
    if (Char.IsLetterOrDigit(c) ||
        c == '.' || c == '_' || c == ' ' || c == '%')
        sb.Append(c);
    }
}
return sb.ToString();

answered Apr 15 '11 at 18:22

Jonathan Wood

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`IsLetterOrDigit` allows *all* Unicode letters and digits. For example, calling it with 'Ѝ' will return `true`. – Jim Mischel Apr 15 '11 at 20:40
@Jim: Yes, I understand that. But while the original question only checked for English alphabet characters, it also didn't address the issue of international characters. It seemed quite possible that `Char.IsLetterOrDigit()` would meet the OP's requirements. – Jonathan Wood Apr 15 '11 at 22:46

score 1 · Answer 7 · answered Apr 15 '11 at 18:28

Cast each char to an int, then compare its ascii code to the ascii table, which you can find all over the internet: http://www.asciitable.com/

    {
        char[] input = txtInput.Text.ToCharArray();
        StringBuilder sbResult = new StringBuilder();

        foreach (char c in input)
        {
            int asciiCode = (int)c;
            if (
                //Space
                asciiCode == 32
                ||
                // Period (.)
                asciiCode == 46
                ||
                // Percentage Sign (%)
                asciiCode == 37
                ||
                // Underscore
                asciiCode == 95
                ||
                ( //0-9, 
                    asciiCode >= 48
                    && asciiCode <= 57
                )
                ||
                ( //A-Z
                    asciiCode >= 65
                    && asciiCode <= 90
                )
                ||
                ( //a-z
                    asciiCode >= 97
                    && asciiCode <= 122
                )
            )
            {
                sbResult.Append(c);
            }
        }

        txtResult.Text = sbResult.ToString();
    }

C# Remove special characters

7 Answers7

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