Performing Culture-Insensitive String Comparisons

By default, the String.Compare method performs culture-sensitive and case-sensitive comparisons. This method also includes several overloads that provide a culture parameter that lets you specify the culture to use, and a comparisonType parameter that lets you specify the comparison rules to use. Calling these methods instead of the default overload removes any ambiguity about the rules used in a particular method call, and makes it clear whether a particular comparison is culture-sensitive or culture-insensitive.

Note

Both overloads of the String.CompareTo method perform culture-sensitive and case-sensitive comparisons; you cannot use this method to perform culture-insensitive comparisons. For code clarity, we recommend that you use the String.Compare method instead.

For culture-sensitive operations, specify the StringComparison.CurrentCulture or StringComparison.CurrentCultureIgnoreCase enumeration value as the comparisonType parameter. If you want to perform a culture-sensitive comparison using a designated culture other than the current culture, specify the CultureInfo object that represents that culture as the culture parameter.

The culture-insensitive string comparisons supported by the String.Compare method are either linguistic (based on the sorting conventions of the invariant culture) or non-linguistic (based on the ordinal value of the characters in the string). Most culture-insensitive string comparisons are non-linguistic. For these comparisons, specify the StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase enumeration value as the comparisonType parameter. For example, if a security decision (such as a user name or password comparison) is based on the result of a string comparison, the operation should be culture-insensitive and non-linguistic to ensure that the result is not affected by the conventions of a particular culture or language. (See Custom Case Mappings and Sorting Rules for an example that demonstrates how culture-sensitive string comparisons can produce inconsistent results.)

Use culture-insensitive linguistic string comparison if you want to handle linguistically relevant strings from multiple cultures in a consistent way. For example, if your application displays words that use multiple character sets in a list box, you might want to display words in the same order regardless of the current culture. For culture-insensitive linguistic comparisons, the .NET Framework defines an invariant culture that is based on the linguistic conventions of English. To perform a culture-insensitive linguistic comparison, specify StringComparison.InvariantCulture or StringComparison.InvariantCultureIgnoreCase as the comparisonType parameter.

The following example performs two culture-insensitive, non-linguistic string comparisons. The first is case-sensitive, but the second is not.

Public Class CompareSample
    Public Shared Sub Main()
        Dim string1 As String = "file" 
        Dim string2 As String = "FILE" 
        Dim compareResult As Integer

        compareResult = String.Compare(string1, string2, _
                                       StringComparison.Ordinal)   
        Console.WriteLine("{0} comparison of '{1}' and '{2}': {3}", _
                          StringComparison.Ordinal, string1, string2, _
                          compareResult) 

        compareResult = String.Compare(string1, string2, _
                                       StringComparison.OrdinalIgnoreCase)
        Console.WriteLine("{0} comparison of '{1}' and '{2}': {3}", _
                          StringComparison.OrdinalIgnoreCase, string1, string2, _
                          compareResult) 
    End Sub 
End Class 
' The example displays the following output: 
'    Ordinal comparison of 'file' and 'FILE': 32 
'    OrdinalIgnoreCase comparison of 'file' and 'FILE': 0

using System;

public class CompareSample
{
    public static void Main()
    {
        string string1 = "file";
        string string2 = "FILE";
        int compareResult = 0;

        compareResult = String.Compare(string1, string2, 
                                       StringComparison.Ordinal);
        Console.WriteLine("{0} comparison of '{1}' and '{2}': {3}", 
                          StringComparison.Ordinal, string1, string2, 
                          compareResult); 

        compareResult = String.Compare(string1, string2, 
                                       StringComparison.OrdinalIgnoreCase);
        Console.WriteLine("{0} comparison of '{1}' and '{2}': {3}", 
                          StringComparison.OrdinalIgnoreCase, string1, string2, 
                          compareResult); 
    }
}
// The example displays the following output: 
//    Ordinal comparison of 'file' and 'FILE': 32 
//    OrdinalIgnoreCase comparison of 'file' and 'FILE': 0

See Also

Concepts

Comparing and Sorting Data for a Specific Culture

Reference

String.Compare

String.CompareTo

Other Resources

Performing Culture-Insensitive String Operations

Best Practices for Using Strings in the .NET Framework

Change History

Date	History	Reason
May 2010	Revised to reflect best practices for handling strings.	Content bug fix.