Articolo
11/18/2011

String.Compare Method (String, Int32, String, Int32, Int32)

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Updated: January 2011

Performs a culture-sensitive comparison of substrings that are extracted from two specified String objects and returns an integer that indicates their relationship to one another in the sort order.

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

Syntax

'Declaration
Public Shared Function Compare ( _
    strA As String, _
    indexA As Integer, _
    strB As String, _
    indexB As Integer, _
    length As Integer _
) As Integer

public static int Compare(
    string strA,
    int indexA,
    string strB,
    int indexB,
    int length
)

Parameters

strA
Type: System.String
The first string to use in the comparison.

indexA
Type: System.Int32
The position of the substring within strA.

strB
Type: System.String
The second string to use in the comparison.

indexB
Type: System.Int32
The position of the substring within strB.

length
Type: System.Int32
The maximum number of characters in the substrings to compare.

Return Value

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

Value	Condition
Less than zero	The substring in strA is less than the substring in strB.
Zero	The substrings are equal, or length is zero.
Greater than zero	The substring in strA is greater than the substring in strB.

Exceptions

Exception	Condition
ArgumentOutOfRangeException	indexA is greater than strA.Length. -or- indexB is greater than strB.Length. -or- indexA, indexB, or length is negative. -or- Either indexA or indexB is nulla null reference (Nothing in Visual Basic), and length is greater than zero.

ArgumentOutOfRangeException

indexA is greater than strA.Length.

-or-

indexB is greater than strB.Length.

-or-

indexA, indexB, or length is negative.

-or-

Either indexA or indexB is nulla null reference (Nothing in Visual Basic), and length is greater than zero.

Remarks

The substrings to compare start in strA at indexA, and in strB at indexB. Both indexA and indexB are zero-based; that is, the first character in strA and strB is at position zero, not position one. The length of the first substring is equal to the length of strA minus indexA plus one. The length of the second substring is equal to the length of strB minus indexB plus one.

The number of characters to compare is the lesser of the lengths of the two substrings, and length. The indexA, indexB, and length parameters must be nonnegative.

The comparison uses the current culture to obtain culture-specific information such as casing rules and the alphabetic order of individual characters. For example, a culture could specify that certain combinations of characters be treated as a single character, or uppercase and lowercase characters be compared in a particular way, or that the sorting order of a character depends on the characters that precede or follow it.

Caution:
The Compare(String, Int32, String, Int32, Int32) method is designed primarily for use in sorting or alphabetizing operations. It should not be used when the primary purpose of the method call is to determine whether two strings are equivalent (that is, when the purpose of the method call is to test for a return value of zero). To determine whether two strings are equivalent, call the Equals method.

The Compare(String, Int32, String, Int32, Int32) method is designed primarily for use in sorting or alphabetizing operations. It should not be used when the primary purpose of the method call is to determine whether two strings are equivalent (that is, when the purpose of the method call is to test for a return value of zero). To determine whether two strings are equivalent, call the Equals method.

The comparison is performed using word sort rules. For more information about word, string, and ordinal sorts, see System.Globalization.CompareOptions.

Caution:
When comparing strings, you should call the Compare method, which requires that you explicitly specify the type of string comparison that the method uses.

One or both comparands can be nulla null reference (Nothing in Visual Basic). 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 substrings have been compared. However, if the two strings compare equal to the end of one string, and the other string has characters remaining, then 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:

Examples

The following code example compares two substrings.

' Sample for String.Compare(String, Int32, String, Int32, Int32)

Class Example
   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      '                       0123456
      Dim str1 As [String] = "machine"
      Dim str2 As [String] = "device"
      Dim str As [String]
      Dim result As Integer

      outputBlock.Text &= vbCrLf
      outputBlock.Text += String.Format("str1 = '{0}', str2 = '{1}'", str1, str2) & vbCrLf
      result = [String].Compare(str1, 2, str2, 0, 2)
      str = IIf(result < 0, "less than", IIf(result > 0, "greater than", "equal to"))
      outputBlock.Text += String.Format("Substring '{0}' in '{1}' is ", str1.Substring(2, 2), str1)
      outputBlock.Text += String.Format("{0} ", str)
      outputBlock.Text += String.Format("substring '{0}' in '{1}'.", str2.Substring(0, 2), str2) & vbCrLf
   End Sub 'Main
End Class 'Sample
'
'This example produces the following results:
'
'str1 = 'machine', str2 = 'device'
'Substring 'ch' in 'machine' is less than substring 'de' in 'device'.
'

// Sample for String.Compare(String, Int32, String, Int32, Int32)
using System;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      //                 0123456
      String str1 = "machine";
      String str2 = "device";
      String str;
      int result;

      outputBlock.Text += "\n";
      outputBlock.Text += String.Format("str1 = '{0}', str2 = '{1}'", str1, str2) + "\n";
      result = String.Compare(str1, 2, str2, 0, 2);
      str = ((result < 0) ? "less than" : ((result > 0) ? "greater than" : "equal to"));
      outputBlock.Text += String.Format("Substring '{0}' in '{1}' is ", str1.Substring(2, 2), str1);
      outputBlock.Text += String.Format("{0} ", str);
      outputBlock.Text += String.Format("substring '{0}' in '{1}'.", str2.Substring(0, 2), str2) + "\n";
   }
}
/*
This example produces the following results:

str1 = 'machine', str2 = 'device'
Substring 'ch' in 'machine' is less than substring 'de' in 'device'.
*/

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Change History

Date	History	Reason
January 2011	Added the recommendation to use an overload that has a StringComparison parameter.	Information enhancement.

Condividi tramite

String.Compare Method (String, Int32, String, Int32, Int32)

Syntax

Parameters

Return Value

Exceptions

Remarks

Examples

Version Information

Silverlight

Silverlight for Windows Phone

XNA Framework

Platforms

See Also

Reference

Change History

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