C# 0 The Complete Reference

Compare( )

 method defined by 

String

.

The String Methods

The

String

 class defines a large number of methods, and many of the methods have two 

or more overloaded forms. For this reason, it is neither practical nor useful to list them all. 

Instead, several of the more commonly used methods will be presented, along with examples 

that illustrate them.

Comparing Strings

Perhaps the most frequently used string-handling operation is the comparison of one string 

to another. Because of its importance, 

String

 provides a wide array of comparison methods. 

These are shown in Table 22-1. Be aware that string comparisons are sensitive to cultural 

differences. Comparison methods that do not pass cultural information use the currently 

selected cultural settings.

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Method

Description

public static int

    Compare(string 

str1

, string 

str2

)

Compares the string referred to by 

str1

 with 

str2.

Returns greater than zero if 

str1

 is greater than 

str2,

 less than zero if 

str1

 is less than 

str2,

 and 

zero if 

str1

 and 

str2

 are equal.

public static int

    Compare(string 

str1

, string 

str2

,

                  bool 

ignoreCase

)

Compares the string referred to by 

str1

 with 

str2.

Returns greater than zero if 

str1

 is greater than 

str2,

 less than zero if 

str1

 is less than 

str2,

 and 

zero if 

str1

 and 

str2

 are equal. If 

ignoreCase

 is 

true

, the comparison ignores case differences. 

Other wise, case differences matter.

public static int

    Compare(string 

str1

, string 

str2

,

                  StringComparison 

how

)

Compares the string referred to by 

str1

 with 

str2.

Returns greater than zero if 

str1

 is greater than 

str2,

 less than zero if 

str1

 is less than 

str2,

 and 

zero if 

str1

 and 

str2

 are equal. How the comparison 

is per formed is specified by 

how.

public static int

    Compare(string 

str1

, string 

str2

,

                  bool 

ignoreCase

,

                  CultureInfo 

ci

 )

Compares the string referred to by 

str1

 with 

str2

using the cultural information passed in 

ci.

 Returns 

greater than zero if 

str1

 is greater than 

str2,

 less 

than zero if 

str1

 is less than 

str2,

 and zero if 

str1

 and 

str2

 are equal. If 

ignoreCase

 is 

true

, the 

comparison ignores case differences. Other wise, 

case differences matter. The 

CultureInfo

 class is 

defined in the 

System.Globalization

 namespace.

public static int

    Compare(string 

str1

, int 

star t1

,

                  string 

str2

, int 

star t2

,

                  int 

count

)

Compares por tions of the strings referred to by 

str1

and

str2.

 The comparison begins at 

str1

[

star t1

] and 

str2

[

star t2

] and runs for 

count

 characters. Returns 

greater than zero if 

str1

 is greater than 

str2,

 less 

than zero if 

str1

 is less than 

str2,

 and zero if 

str1

and

str2

 are equal.

public static int

    Compare(string 

str1

, int 

star t1

,

                  string 

str2

, int 

star t2

,

                  int 

count

,

                  bool 

ignoreCase

)

Compares portions of the strings referred to by 

str1

and

str2.

 The comparison begins at 

str1

[

start1

] and 

str2

[

start2

] and runs for 

count

 characters. Returns 

greater than zero if 

str1

 is greater than 

str2,

 less 

than zero if 

str1

 is less than 

str2,

 and zero if 

str1

 and 

str2

 are equal. If 

ignoreCase

 is 

true

, the comparison 

ignores case differences. Otherwise, case differences 

matter.

public static int

    Compare(string 

str1

, int 

star t1

,

                  string 

str2

, int 

star t2

,

                  int 

count

,

                  StringComparison 

how

)

Compares por tions of the strings referred to by 

str1

and

str2.

 The comparison begins at 

str1

[

star t1

]

and

str2

[

star t2

] and runs for 

count

 characters. 

Returns greater than zero if 

str1

 is greater than 

str2,

 less than zero if 

str1

 is less than 

str2,

 and 

zero if 

str1

 and 

str2

 are equal. How the comparison 

is per formed is specified by 

how.

T

ABLE

 22-1 

The

String

 Comparison Methods

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Of the comparison methods, the 

Compare( )

 method is the most versatile. It can 

compare two strings in their entirety or in parts. It can use case-sensitive comparisons 

or ignore case. In general, string comparisons use dictionary order to determine whether 

one string is greater than, equal to, or less than another. You can also specify cultural 

information that governs the comparison. The following program demonstrates several 

versions of 

Compare( )

:

// Compare strings.

using System;

class CompareDemo {

  static void Main() {

    string str1 = "one";

    string str2 = "one";

T

ABLE

 22-1 

The

String

 Comparison Methods 

(continued)

public static int

    Compare(string 

str1

, int 

star t1

,

                  string 

str2

, int 

star t2

,

                  int 

count

,

                  bool 

ignoreCase

,

                  CultureInfo 

ci

)

Compares por tions of the strings referred to by 

str1

 and 

str2

 using the cultural information passed 

in

ci.

 The comparison begins at 

str1

[

star t1

] and 

str2

[

star t2

] and runs for 

count

 characters. Returns 

greater than zero if 

str1

 is greater than 

str2,

 less 

than zero if 

str1

 is less than 

str2,

 and zero if 

str1

 and 

str2

 are equal. If 

ignoreCase

 is true, the 

comparison ignores case differences. Other wise, 

case differences matter. The 

CultureInfo

 class is 

defined in the 

System.Globalization

namespace.

public static int

    CompareOrdinal(string 

str1

, string 

str2

)

Compares the string referred to by 

str1

 with 

str2

independently of culture, region, or language. 

Returns greater than zero if 

str1

 is greater than 

str2,

 less than zero if 

str1

 is less than 

str2,

 and 

zero if 

str1

 and 

str2

 are equal.

public static int

    CompareOrdinal(string 

str1

, int 

star t1

,

                            string 

str2

, int 

star t2

,

                            int 

count

)

Compares por tions of the strings referred to by 

str1

 and 

str2

 independently of culture, region, or 

language. The comparison begins at 

str1

[

star t1

]

and

str2

[

star t2

] and runs for 

count

 characters. 

Returns greater than zero if 

str1

 is greater than 

str2,

 less than zero if 

str1

 is less than 

str2,

 and 

zero if 

str1

 and 

str2

 are equal.

public int CompareTo(object 

str

)

Compares the invoking string with 

str.

 Returns 

greater than zero if the invoking string is greater 

than

str,

 less than zero if the invoking string is less 

than

str,

 and zero if the two are equal.

public int CompareTo(string 

str

)

Compares the invoking string with 

str.

 Returns 

greater than zero if the invoking string is greater 

than

str,

 less than zero if the invoking string is less 

than

str,

 and zero if the two are equal.

Method

Description

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    string str3 = "ONE";

    string str4 = "two";

    string str5 = "one, too";

    if(String.Compare(str1, str2) == 0)

      Console.WriteLine(str1 + " and " + str2 +

                        " are equal.");

    else

      Console.WriteLine(str1 + " and " + str2 +

                        " are not equal.");

    if(String.Compare(str1, str3) == 0)

      Console.WriteLine(str1 + " and " + str3 +

                        " are equal.");

    else

      Console.WriteLine(str1 + " and " + str3 +

                        " are not equal.");

    if(String.Compare(str1, str3, true) == 0)

      Console.WriteLine(str1 + " and " + str3 +

                        " are equal ignoring case.");

    else

      Console.WriteLine(str1 + " and " + str3 +

                        " are not equal ignoring case.");

     if(String.Compare(str1, str5) == 0)

      Console.WriteLine(str1 + " and " + str5 +

                        " are equal.");

    else

      Console.WriteLine(str1 + " and " + str5 +

                        " are not equal.");

    if(String.Compare(str1, 0, str5, 0, 3) == 0)

      Console.WriteLine("First part of " + str1 + " and " +

                        str5 + " are equal.");

    else

      Console.WriteLine("First part of " + str1 + " and " +

                        str5 + " are not equal.");

    int result = String.Compare(str1, str4);

    if(result < 0)

      Console.WriteLine(str1 + " is less than " + str4);

    else if(result > 0)

      Console.WriteLine(str1 + " is greater than " + str4);

    else

      Console.WriteLine(str1 + " equals " + str4);

  }

}

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