StringComparer Class
Represents a string comparison operation that uses specific case and culture-based or ordinal comparison rules.
Assembly: mscorlib (in mscorlib.dll)
An object derived from the StringComparer class embodies string-based comparison, equality, and hash code operations that take into account both case and culture-specific comparison rules. You can use the StringComparer class to create a type-specific comparison to sort the elements in a generic collection. Classes such as Hashtable, Dictionary(Of TKey, TValue), SortedList, and SortedList(Of TKey, TValue) use the StringComparer class for sorting purposes.
A comparison operation that is represented by the StringComparer class is defined to be either case-sensitive or case-insensitive, and use either word (culture-sensitive) or ordinal (culture-insensitive) comparison rules. For more information about word and ordinal comparison rules, see System.Globalization.CompareOptions.
Implemented Properties
You might be confused about how to use the StringComparer class properties because of a seeming contradiction. The StringComparer class is declared abstract (MustInherit in Visual Basic), which means its members can be invoked only on an object of a class derived from the StringComparer class. The contradiction is that each property of the StringComparer class is declared static (Shared in Visual Basic), which means the property can be invoked without first creating a derived class.
You can call a StringComparer property directly because each property actually returns an instance of an anonymous class that is derived from the StringComparer class. Consequently, the type of each property value is StringComparer, which is the base class of the anonymous class, not the type of the anonymous class itself. Each StringComparer class property returns a StringComparer object that supports predefined case and comparison rules.
The following code example demonstrates the properties and the Create method of the StringComparer class. The example illustrates how different StringComparer objects sort three versions of the Latin letter I.
' This code example demonstrates members of the System.StringComparer class. Imports System Imports System.Collections Imports System.Collections.Generic Imports System.Globalization Imports System.Threading Class Sample Public Shared Sub Main() ' Create a list of string. Dim list As New List(Of String) ' Get the tr-TR (Turkish-Turkey) culture. Dim turkish As New CultureInfo("tr-TR") ' Get the culture that is associated with the current thread. Dim thisCulture As CultureInfo = Thread.CurrentThread.CurrentCulture ' Get the standard StringComparers. Dim invCmp As StringComparer = StringComparer.InvariantCulture Dim invICCmp As StringComparer = StringComparer.InvariantCultureIgnoreCase Dim currCmp As StringComparer = StringComparer.CurrentCulture Dim currICCmp As StringComparer = StringComparer.CurrentCultureIgnoreCase Dim ordCmp As StringComparer = StringComparer.Ordinal Dim ordICCmp As StringComparer = StringComparer.OrdinalIgnoreCase ' Create a StringComparer that uses the Turkish culture and ignores case. Dim turkICComp As StringComparer = StringComparer.Create(turkish, True) ' Define three strings consisting of different versions of the letter I. ' LATIN CAPITAL LETTER I (U+0049) Dim capitalLetterI As String = "I" ' LATIN SMALL LETTER I (U+0069) Dim smallLetterI As String = "i" ' LATIN SMALL LETTER DOTLESS I (U+0131) Dim smallLetterDotlessI As String = "ı" ' Add the three strings to the list. list.Add(capitalLetterI) list.Add(smallLetterI) list.Add(smallLetterDotlessI) ' Display the original list order. Display(list, "The original order of the list entries...") ' Sort the list using the invariant culture. list.Sort(invCmp) Display(list, "Invariant culture...") list.Sort(invICCmp) Display(list, "Invariant culture, ignore case...") ' Sort the list using the current culture. Console.WriteLine("The current culture is ""{0}"".", thisCulture.Name) list.Sort(currCmp) Display(list, "Current culture...") list.Sort(currICCmp) Display(list, "Current culture, ignore case...") ' Sort the list using the ordinal value of the character code points. list.Sort(ordCmp) Display(list, "Ordinal...") list.Sort(ordICCmp) Display(list, "Ordinal, ignore case...") ' Sort the list using the Turkish culture, which treats LATIN SMALL LETTER ' DOTLESS I differently than LATIN SMALL LETTER I. list.Sort(turkICComp) Display(list, "Turkish culture, ignore case...") End Sub 'Main Public Shared Sub Display(ByVal lst As List(Of String), ByVal title As String) Dim c As Char Dim s As String Dim codePoint As Integer Console.WriteLine(title) For Each s In lst c = s(0) codePoint = Convert.ToInt32(c) Console.WriteLine("0x{0:x}", codePoint) Next s Console.WriteLine() End Sub 'Display End Class 'Sample ' 'This code example produces the following results: ' 'The original order of the list entries... '0x49 '0x69 '0x131 ' 'Invariant culture... '0x69 '0x49 '0x131 ' 'Invariant culture, ignore case... '0x49 '0x69 '0x131 ' 'The current culture is "en-US". 'Current culture... '0x69 '0x49 '0x131 ' 'Current culture, ignore case... '0x49 '0x69 '0x131 ' 'Ordinal... '0x49 '0x69 '0x131 ' 'Ordinal, ignore case... '0x69 '0x49 '0x131 ' 'Turkish culture, ignore case... '0x131 '0x49 '0x69 '
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