Manipulation and Regular Expressions of Strings

The String class provides a host of methods for comparing, searching, and manipulating strings.

Method or property	Explanation
Chars	Property that returns the string indexer
Compare()	Overloaded public static method that compares two strings
Copy()	Public static method that creates a new string by copying another
Equals()	Overloaded public static and instance method that determines if two strings have the same value
Format()	Overloaded public static method that formats a string using a format specification
Length	Property that returns the number of characters in the instance
PadLeft()	Right-aligns the characters in the string, padding to the left with spaces or a specified character
PadRight()	Left-aligns the characters in the string, padding to the right with spaces or a specified character
Remove()	Deletes the specified number of characters
Split()	Divides a string, returning the substrings delimited by the specified characters
StartsWith()	Indicates if the string starts with the specified characters
Substring()	Retrieves a substring
ToCharArray()	Copies the characters from the string to a character array
ToLower()	Returns a copy of the string in lowercase
ToUpper()	Returns a copy of the string in uppercase
Trim()	Removes all occurrences of a set of specified characters from beginning and end of the string
TrimEnd()	Behaves like Trim(), but only at the end
TrimStart()	Behaves like Trim(), but only at the start

Comparing Strings

The Compare() method is overloaded. The first version takes two strings and returns a negative number if the first string is alphabetically before the second, a positive number if the first string is alphabetically after the second, and zero if they are equal. The second version works just like the first but is case-insensitive.

Regular Expressions

Regular expressions are a powerful language for describing and manipulating text. Underlying regular expressions is a technique called pattern matching, which involves comparing one string to another, or comparing a series of wildcards that represent a type of string to a literal string. A regular expression is applied to a string — that is, to a set of characters. Often that string is an entire text document.

The result of applying a regular expression to a string is either to return a substring or to return a new string representing a modification of some part of the original string. (Remember that string objects are immutable and so cannot be changed by the regular expression.)

By applying a properly constructed regular expression to the following string:

One,Two,Three Liberty Associates, Inc.

you can return any or all of its substrings (e.g., Liberty or One) or modified versions of its substrings (e.g., LIBeRtY or OnE). What the regular expression does is determined by the syntax of the regular expression itself.

A regular expression consists of two types of characters: literals and metacharacters. A literal is a character you want to match in the target string. A metacharacter is a special symbol that acts as a command to the regular expression parser. The parser is the engine responsible for understanding the regular expression. For example, if you create a regular expression:

^(From|To|Subject|Date):

this will match any substring with the letters "From", "To", "Subject", or "Date" so long as those letters start a new line (^) and end with a colon (:).

The caret (^) indicates to the regular expression parser that the string you're searching for must begin a new line. The letters "From" and "To" are literals, and the metacharacters left and right parentheses ( (, ) ) and vertical bar (|) are all used to group sets of literals and indicate that any of the choices should match. Thus you would read the following line as "match any string that begins a new line, followed by any of the four literal strings From, To, Subject, or Date, and followed by a colon":

^(From|To|Subject|Date):

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