Recipe 2.1. Determining the Kind of Character a char ContainsProblemYou have a variable of type char and wish to determine the kind of character it containsa letter, digit, number, punctuation character, control character, separator character, symbol, whitespace, or surrogate character. Similarly, you have a string variable and want to determine the kind of character in one or more positions within this string. SolutionTo determine the value of a char, use the built-in static methods on the System.Char structure shown here: Char.IsControl Char.IsDigit Char.IsLetter Char.IsNumber Char.IsPunctuation Char.IsSeparator Char.IsSurrogate Char.IsSymbol Char.IsWhitespace DiscussionThe following examples demonstrate how to use the methods shown in the Solution section in a function to return the kind of a character. First, create an enumeration to define the various types of characters: public enum CharKind { Letter, Number, Punctuation, Unknown } Next, create a method that contains the logic to determine the type of a character and to return a CharKind enumeration value indicating that type: public static CharKind GetCharKind(char theChar) { if (Char.IsLetter(theChar)) { return CharKind.Letter; } else if (Char.IsNumber(theChar)) { return CharKind.Number; } else if (Char.IsPunctuation(theChar)) { return CharKind.Punctuation; } else { return CharKind.Unknown; } } If, however, a character in a string needs to be evaluated, use the overloaded static methods on the char structure. The following code modifies the GetCharKind method to accept a string variable and a character position in that string. The character position determines which character in the string is evaluated. public static CharKind GetCharKindInString(string theString, int charPosition) { if (Char.IsLetter(theString, charPosition)) { return CharKind.Letter; } else if (Char.IsNumber(theString, charPosition)) { return CharKind.Number; } else if (Char.IsPunctuation(theString, charPosition)) { return CharKind.Punctuation; } else { return CharKind.Unknown; } } The GetCharKind method accepts a character as a parameter and performs a series of tests on that character using the Char type's built-in static methods. An enumeration of all the different types of characters is defined and is returned by the GetCharKind method. Table 2-1 describes each of the static Char methods.
The following code example determines whether the fifth character (the charPosition parameter is zero-based) in the string is a digit: if (GetCharKind("abcdefg", 4) == CharKind.Digit) {…} In Version 2.0 of the .NET Framework, a few extra Is* functions were added to augment the existing methods. If the character in question is a letter (i.e., the IsLetter method returns true), you can determine if the letter is uppercase or lowercase by using the methods in Table 2-2.
If the character in question is a surrogate (i.e., the IsSurrogate method returns true), you can use the methods in Table 2-3 to get more information on the surrogate character.
In addition to these surrogate methods, an additional method, IsSurrogatePair, returns true only if two characters create a surrogate pairthat is, one character is a high surrogate and one character is a low surrogate. The final addition to this group of methods is the IsLetterOrDigit method, which returns TRue only if the character in question is either a letter or a digit. To determine if the character is either a letter or a digit, use the IsLetter and IsDigit methods. See AlsoSee the "Char Structure" topic in the MSDN documentation. |