这并不是最优的性能，而是一种非常直接的Linq方法:

string strippedString = new string(
    yourString.Where(c => c <= sbyte.MaxValue).ToArray()
    );

缺点是，所有“幸存的”字符首先被放入char[]类型的数组中，然后在字符串构造函数不再使用它后将其丢弃。

Necromancing。 此外，bzlm的方法可以用来删除不属于任意字符集的字符，而不仅仅是ASCII:

// https://en.wikipedia.org/wiki/Code_page#EBCDIC-based_code_pages
// https://en.wikipedia.org/wiki/Windows_code_page#East_Asian_multi-byte_code_pages
// https://en.wikipedia.org/wiki/Chinese_character_encoding
System.Text.Encoding encRemoveAllBut = System.Text.Encoding.ASCII;
encRemoveAllBut = System.Text.Encoding.GetEncoding(System.Globalization.CultureInfo.InstalledUICulture.TextInfo.ANSICodePage); // System-encoding
encRemoveAllBut = System.Text.Encoding.GetEncoding(1252); // Western European (iso-8859-1)
encRemoveAllBut = System.Text.Encoding.GetEncoding(1251); // Windows-1251/KOI8-R
encRemoveAllBut = System.Text.Encoding.GetEncoding("ISO-8859-5"); // used by less than 0.1% of websites
encRemoveAllBut = System.Text.Encoding.GetEncoding(37); // IBM EBCDIC US-Canada
encRemoveAllBut = System.Text.Encoding.GetEncoding(500); // IBM EBCDIC Latin 1
encRemoveAllBut = System.Text.Encoding.GetEncoding(936); // Chinese Simplified
encRemoveAllBut = System.Text.Encoding.GetEncoding(950); // Chinese Traditional
encRemoveAllBut = System.Text.Encoding.ASCII; // putting ASCII again, as to answer the question 

// https://stackoverflow.com/questions/123336/how-can-you-strip-non-ascii-characters-from-a-string-in-c
string inputString = "RäksmörПривет, мирgås";
string asAscii = encRemoveAllBut.GetString(
    System.Text.Encoding.Convert(
        System.Text.Encoding.UTF8,
        System.Text.Encoding.GetEncoding(
            encRemoveAllBut.CodePage,
            new System.Text.EncoderReplacementFallback(string.Empty),
            new System.Text.DecoderExceptionFallback()
            ),
        System.Text.Encoding.UTF8.GetBytes(inputString)
    )
);

System.Console.WriteLine(asAscii);

对于那些只想消除口音的人来说: (注意，因为正常化!=拉丁化!=罗马化)

// string str = Latinize("(æøå âôû?aè");
public static string Latinize(string stIn)
{
    // Special treatment for German Umlauts
    stIn = stIn.Replace("ä", "ae");
    stIn = stIn.Replace("ö", "oe");
    stIn = stIn.Replace("ü", "ue");

    stIn = stIn.Replace("Ä", "Ae");
    stIn = stIn.Replace("Ö", "Oe");
    stIn = stIn.Replace("Ü", "Ue");
    // End special treatment for German Umlauts

    string stFormD = stIn.Normalize(System.Text.NormalizationForm.FormD);
    System.Text.StringBuilder sb = new System.Text.StringBuilder();

    for (int ich = 0; ich < stFormD.Length; ich++)
    {
        System.Globalization.UnicodeCategory uc = System.Globalization.CharUnicodeInfo.GetUnicodeCategory(stFormD[ich]);

        if (uc != System.Globalization.UnicodeCategory.NonSpacingMark)
        {
            sb.Append(stFormD[ich]);
        } // End if (uc != System.Globalization.UnicodeCategory.NonSpacingMark)

    } // Next ich


    //return (sb.ToString().Normalize(System.Text.NormalizationForm.FormC));
    return (sb.ToString().Normalize(System.Text.NormalizationForm.FormKC));
} // End Function Latinize

string s = "søme string";
s = Regex.Replace(s, @"[^\u0000-\u007F]+", string.Empty);

^是not运算符。它告诉正则表达式去查找所有不匹配的，而不是所有匹配的。\u####-\u####表示匹配的字符。\u0000-\u007F相当于utf-8或unicode中的前128个字符，这些字符总是ascii字符。因此，您匹配每个非ascii字符(因为not)，并对所有匹配的字符进行替换。

(正如Gordon Tucker在2009年12月11日21:11的评论中所解释的那样)

这并不是最优的性能，而是一种非常直接的Linq方法:

string strippedString = new string(
    yourString.Where(c => c <= sbyte.MaxValue).ToArray()
    );

缺点是，所有“幸存的”字符首先被放入char[]类型的数组中，然后在字符串构造函数不再使用它后将其丢弃。

不需要正则表达式。只要使用编码…

sOutput = System.Text.Encoding.ASCII.GetString(System.Text.Encoding.ASCII.GetBytes(sInput));

public string ReturnCleanASCII(string s)
    {
        StringBuilder sb = new StringBuilder(s.Length);
        foreach (char c in s)
        {
            if ((int)c > 127) // you probably don't want 127 either
                continue;
            if ((int)c < 32)  // I bet you don't want control characters 
                continue;
            if (c == '%')
                continue;
            if (c == '?')
                continue;
            sb.Append(c);
        }
        return sb.ToString();
    }