6.5 Procedural- and Expression-Based Patterns
Generally, users of regular expressions fall into one of two groups.
The first group tends to use minimal regular expressions that provide
matching or grouping behaviors, and then write procedural code to
perform some iterative behavior. The second group tries to utilize
the maximum power and functionality of the expression-processing
engine itself, with as little procedural logic as possible. For most
of us, the best answer is somewhere in between.
We'll now explore the trade-offs in complexity and
performance of these two approaches.
6.5.1 Procedural-Based Patterns
A common processing need is
to
match certain parts of a string and perform some processing. So,
here's an example that matches words within a string
and capitalizes them:
using System;
using System.Text.RegularExpressions;
class ProceduralFun {
static void Main( ) {
string txt = "the quick red fox jumped over the lazy brown dog.";
Console.WriteLine("text=["+txt+"]");
string res = "";
string pat = @"\w+|\W+";
// Loop through all the matches
foreach (Match m in Regex.Matches(txt, pat)) {
string s = m.ToString( );
// If the first char is lower case, capitalize it
if (char.IsLower(s[0]))
s = char.ToUpper(s[0])+s.Substring(1, s.Length-1);
res += s; // Collect the text
}
Console.WriteLine("result=["+res+"]");
}
}
As you can see, you use the C# foreach statement
to process the set of matches found, and perform some processing (in
this case, creating a new result string).
The output of the sample is:
text=[the quick red fox jumped over the lazy brown dog.]
result=[The Quick Red Fox Jumped Over The Lazy Brown Dog.]
6.5.2 Expression-Based Patterns
Another way to implement the previous
example is by providing a
MatchEvaluator, which processes it as a single
result set.
So the new sample looks like:
using System;
using System.Text.RegularExpressions;
class ExpressionFun {
static string CapText(Match m) {
// Get the matched string
string s = m.ToString( );
// If the first char is lower case, capitalize it
if (char.IsLower(s[0]))
return char.ToUpper(s[0]) + s.Substring(1, s.Length-1);
return s;
}
static void Main( ) {
string txt = "the quick red fox jumped over the lazy brown dog.";
Console.WriteLine("text=[" + txt + "]");
string pat = @"\w+";
MatchEvaluator me = new MatchEvaluator(CapText);
string res = Regex.Replace(txt, pat, me);
Console.WriteLine("result=[" + res + "]");
}
}
Also of note is that the pattern is simplified, since we need only to
modify the words, not the nonwords.
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