String.Compare Method (String, String, StringComparison)

May 11, 2014

Compares two specified String objects using the specified string comparison options and returns an integer that indicates their relationship to one another in the sort order.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public static int Compare(
	string strA,
	string strB,
	StringComparison comparisonType
)

Parameters

strA
Type: System.String
The first string to compare.
strB
Type: System.String
The second string to compare.
comparisonType
Type: System.StringComparison
One of the enumeration values that specifies the rules to use in the comparison.

Return Value

Type: System.Int32
A 32-bit signed integer indicating the lexical relationship between the two comparands.

Value

Condition

Less than zero

strA is less than strB.

Zero

strA equals strB.

Greater than zero

strA is greater than strB.

ExceptionCondition
ArgumentException

comparisonType is not a StringComparison value.

NotSupportedException

StringComparison is not supported.

The comparisonType parameter indicates whether the comparison should use the current or invariant culture, honor or ignore the case of the comparands, or use word (culture-sensitive) or ordinal (culture-insensitive) sort rules.

One or both comparands can be null. By definition, any string, including the empty string (""), compares greater than a null reference; and two null references compare equal to each other.

The comparison terminates when an inequality is discovered or both strings have been compared. However, if the two strings compare equal to the end of one string, and the other string has characters remaining, the string with remaining characters is considered greater. The return value is the result of the last comparison performed.

Unexpected results can occur when comparisons are affected by culture-specific casing rules. For example, in Turkish, the following example yields the wrong results because the file system in Turkish does not use linguistic casing rules for the letter 'i' in "file".

Compare the path name to "file" using an ordinal comparison. The correct code to do this is as follows:

The following code example compares three versions of the letter 'I'. The results are affected by the choice of culture, whether case is ignored, and whether an ordinal comparison is performed.


// This example demonstrates the 
// System.String.Compare(String, String, StringComparison) method.

using System;
using System.Threading;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string intro = "Compare three versions of the letter I using different " +
                     "values of StringComparison.";

      // Define an array of strings where each element contains a version of the 
      // letter I. (An array of strings is used so you can easily modify this 
      // code example to test additional or different combinations of strings.)  

      string[] threeIs = new string[3];
      // LATIN SMALL LETTER I (U+0069)
      threeIs[0] = "\u0069";
      // LATIN SMALL LETTER DOTLESS I (U+0131)
      threeIs[1] = "\u0131";
      // LATIN CAPITAL LETTER I (U+0049)
      threeIs[2] = "\u0049";

      string[] unicodeNames = 
             {
             "LATIN SMALL LETTER I (U+0069)", 
             "LATIN SMALL LETTER DOTLESS I (U+0131)", 
             "LATIN CAPITAL LETTER I (U+0049)"
             };

      StringComparison[] scValues = {
        StringComparison.CurrentCulture,
        StringComparison.CurrentCultureIgnoreCase,
        StringComparison.InvariantCulture,
        StringComparison.InvariantCultureIgnoreCase,
        StringComparison.Ordinal,
        StringComparison.OrdinalIgnoreCase };

      //
      outputBlock.Text += intro + "\n";

      // Display the current culture because the culture-specific comparisons
      // can produce different results with different cultures.
      outputBlock.Text += String.Format("The current culture is {0}.\n",
                         Thread.CurrentThread.CurrentCulture.Name) + "\n";

      // Determine the relative sort order of three versions of the letter I. 
      foreach (StringComparison sc in scValues)
      {
         outputBlock.Text += String.Format("StringComparison.{0}:", sc) + "\n";

         // LATIN SMALL LETTER I (U+0069) : LATIN SMALL LETTER DOTLESS I (U+0131)
         Test(outputBlock, 0, 1, sc, threeIs, unicodeNames);

         // LATIN SMALL LETTER I (U+0069) : LATIN CAPITAL LETTER I (U+0049)
         Test(outputBlock, 0, 2, sc, threeIs, unicodeNames);

         // LATIN SMALL LETTER DOTLESS I (U+0131) : LATIN CAPITAL LETTER I (U+0049)
         Test(outputBlock, 1, 2, sc, threeIs, unicodeNames);

         outputBlock.Text += "\n";
      }
   }

   protected static void Test(System.Windows.Controls.TextBlock outputBlock, int x, int y,
                              StringComparison comparison,
                              string[] testI, string[] testNames)
   {
      string resultFmt = "{0} is {1} {2}";
      string result = "equal to";
      int cmpValue = 0;
      //
      cmpValue = String.Compare(testI[x], testI[y], comparison);
      if (cmpValue < 0)
         result = "less than";
      else if (cmpValue > 0)
         result = "greater than";
      outputBlock.Text += String.Format(resultFmt, testNames[x], result, testNames[y]) + "\n";
   }
}

/*
This code example produces the following results:

Compare three versions of the letter I using different values of StringComparison.
The current culture is en-US.

StringComparison.CurrentCulture:
LATIN SMALL LETTER I (U+0069) is less than LATIN SMALL LETTER DOTLESS I (U+0131)
LATIN SMALL LETTER I (U+0069) is less than LATIN CAPITAL LETTER I (U+0049)
LATIN SMALL LETTER DOTLESS I (U+0131) is greater than LATIN CAPITAL LETTER I (U+0049)

StringComparison.CurrentCultureIgnoreCase:
LATIN SMALL LETTER I (U+0069) is less than LATIN SMALL LETTER DOTLESS I (U+0131)
LATIN SMALL LETTER I (U+0069) is equal to LATIN CAPITAL LETTER I (U+0049)
LATIN SMALL LETTER DOTLESS I (U+0131) is greater than LATIN CAPITAL LETTER I (U+0049)

StringComparison.InvariantCulture:
LATIN SMALL LETTER I (U+0069) is less than LATIN SMALL LETTER DOTLESS I (U+0131)
LATIN SMALL LETTER I (U+0069) is less than LATIN CAPITAL LETTER I (U+0049)
LATIN SMALL LETTER DOTLESS I (U+0131) is greater than LATIN CAPITAL LETTER I (U+0049)

StringComparison.InvariantCultureIgnoreCase:
LATIN SMALL LETTER I (U+0069) is less than LATIN SMALL LETTER DOTLESS I (U+0131)
LATIN SMALL LETTER I (U+0069) is equal to LATIN CAPITAL LETTER I (U+0049)
LATIN SMALL LETTER DOTLESS I (U+0131) is greater than LATIN CAPITAL LETTER I (U+0049)

StringComparison.Ordinal:
LATIN SMALL LETTER I (U+0069) is less than LATIN SMALL LETTER DOTLESS I (U+0131)
LATIN SMALL LETTER I (U+0069) is greater than LATIN CAPITAL LETTER I (U+0049)
LATIN SMALL LETTER DOTLESS I (U+0131) is greater than LATIN CAPITAL LETTER I (U+0049)

StringComparison.OrdinalIgnoreCase:
LATIN SMALL LETTER I (U+0069) is less than LATIN SMALL LETTER DOTLESS I (U+0131)
LATIN SMALL LETTER I (U+0069) is equal to LATIN CAPITAL LETTER I (U+0049)
LATIN SMALL LETTER DOTLESS I (U+0131) is greater than LATIN CAPITAL LETTER I (U+0049)

*/


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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