How Can I Compare Strings in C# While Ignoring Accented Characters?

Ignore accented characters when comparing strings in C#

Handling string comparisons with accented characters can be tricky in C#. Consider the following example:

<code class="language-csharp">string s1 = "hello";
string s2 = "héllo";

s1.Equals(s2, StringComparison.InvariantCultureIgnoreCase);
s1.Equals(s2, StringComparison.OrdinalIgnoreCase);</code>

The two strings should be equal, but both statements return false. This is because the accents on letters are treated as different characters. To solve this problem, we can use a technique that removes additional symbols (or accents) before comparing the strings.

Remove additional symbols

Here's a way to remove additional symbols from a string:

<code class="language-csharp">static string RemoveDiacritics(string text)
{
    // 将字符串规范化为 Unicode 规范化形式 D
    string formD = text.Normalize(NormalizationForm.FormD);

    // 创建一个 StringBuilder 来保存结果字符串
    StringBuilder sb = new StringBuilder();

    // 迭代规范化字符串中的字符
    foreach (char ch in formD)
    {
        // 检查字符是否不是非间隔标记
        UnicodeCategory uc = CharUnicodeInfo.GetUnicodeCategory(ch);
        if (uc != UnicodeCategory.NonSpacingMark)
        {
            // 将字符附加到 StringBuilder
            sb.Append(ch);
        }
    }

    // 将 StringBuilder 转换为字符串并将其规范化为 Unicode 规范化形式 C
    return sb.ToString().Normalize(NormalizationForm.FormC);
}</code>

This method first normalizes the string into D form, which splits accented characters into multiple characters. It then iterates over these characters and filters out non-spacing tokens (i.e. accents). Finally, it recombines the remaining characters to form an unaccented string.

To use this method, simply apply it to two strings before comparing them. For example:

<code class="language-csharp">string s1 = "hello";
string s2 = "héllo";

s1.Equals(RemoveDiacritics(s2), StringComparison.InvariantCultureIgnoreCase);  // True</code>

This will correctly evaluate to true, considering the accented "e" in "héllo" to be equivalent to the unaccented "e" in "hello".

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