How Can I Perform Case-Insensitive String Comparisons in C# While Ignoring Accents?

Handling Accents and Case in C# String Comparisons

C# string comparisons can be complicated by accented characters and case sensitivity. This article demonstrates how to perform case-insensitive comparisons while also ignoring diacritical marks (accents).

Accented characters are often treated differently than their non-accented counterparts, leading to inaccurate comparisons. To address this, we can preprocess strings to remove accents before comparison. The following RemoveDiacritics function uses Unicode normalization to achieve this:

static string RemoveDiacritics(string text)
{
    string formD = text.Normalize(NormalizationForm.FormD);
    StringBuilder sb = new StringBuilder();

    foreach (char ch in formD)
    {
        UnicodeCategory uc = CharUnicodeInfo.GetUnicodeCategory(ch);
        if (uc != UnicodeCategory.NonSpacingMark)
        {
            sb.Append(ch);
        }
    }

    return sb.ToString().Normalize(NormalizationForm.FormC);
}

This function normalizes the input string and then iterates through its characters, removing any non-spacing marks (accents). The result is a string with accents removed.

Now, to perform a case-insensitive comparison ignoring accents, simply apply this function to your strings before using Equals:

string s1 = "résumé";
string s2 = "resume";

bool areEqual = RemoveDiacritics(s1).Equals(RemoveDiacritics(s2), StringComparison.OrdinalIgnoreCase); // true

Using StringComparison.OrdinalIgnoreCase provides a culture-insensitive case-insensitive comparison, ensuring consistent results across different systems. This approach ensures that strings with and without accents are treated as equivalent when performing case-insensitive comparisons, improving the accuracy and robustness of your application logic.

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