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String.Compare Method (String, String, StringComparison)

Compares two specified String objects using the specified rules, and returns an integer that indicates their relative position 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 that indicates the lexical relationship between the two comparands.

Value

Condition

Less than zero

strA precedes strB in the sort order.

Zero

strA is in the same position as strB in the sort order.

Greater than zero

strA follows strB in the sort order.

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".

static bool IsFileURI(String path)
{
    return (String.Compare(path, 0, "file:", 0, 5, true) == 0);
}

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

static bool IsFileURI(String path)
{
    return (String.Compare(path, 0, "file:", 0, 5, StringComparison.OrdinalIgnoreCase) == 0);
}

Notes to Callers

Character sets include ignorable characters. The Compare(String, String, StringComparison) method does not consider such characters when it performs a culture-sensitive comparison. To recognize ignorable characters in your comparison, supply a value of StringComparison.Ordinal or OrdinalIgnoreCase for the comparisonType parameter.

The following 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 Sample 
{
    public static void Main() 
    {
    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 };

//
    Console.Clear();
    Console.WriteLine(intro);

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

// Determine the relative sort order of three versions of the letter I.  
    foreach (StringComparison sc in scValues)
        {
        Console.WriteLine("StringComparison.{0}:", sc);

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

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

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

        Console.WriteLine();
        }
    }

    protected static void Test(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";
    Console.WriteLine(resultFmt, testNames[x], result, testNames[y]);
    }
}

/*
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)

*/

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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