C# 5.0 Programmer's Reference

480 ❘ CHAPTER 21 Regular Expressions
{
}
try
{
if (Regex.IsMatch(inputTextBox.Text, patternTextBox.Text))
resultLabel.Text = "Match";
else
resultLabel.Text = "No match";
}
catch (Exception ex)
{
resultLabel.Text = ex.Message;
}
The code passes the Regex.IsMatch method the string to validate and the regular expression. The
method returns true if the string satisfies the expression. The program then displays an appropriate
message in resultLabel.
This example uses a try catch block to protect itself from improperly formed regular expressions.
For example, suppose you want to use the expression (.)\1 to detect repeated characters. At one
point while you’re typing you will have entered just (, which is not a valid regular expression.
Finding Matches
The MatchPattern example program described in the preceding
section determines whether a string satisfies a regular expression.
For example, it can use the pattern (.)\1 to verify that the string
bookkeeper contains a double letter. However, that program
won’t tell you where the double letter is. In this example, bookkeeper
contains three double letters: oo, kk, and ee.
The Regex class’s Matches method can give you information
about places where a string matches a regular expression. The
FindMatches example program, which is available for download
and shown in Figure 21-2, displays the parts of a string that
match a pattern.
The FindMatches program uses the following code to locate matches.
// Display matches.
private void FindMatches()
{
try
{
// Make the regex object.
Regex regex = new Regex(patternTextBox.Text);
// Find the matches.
string matches = "";
foreach (Match match in regex.Matches(inputTextBox.Text))
{
Figure 21-2: The FindMatches
example program finds the parts
of a string that match a pattern.
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