C# removing comments from a string

问题

I'm using WinForms NET 2.0. I am coding a small function to trim comments from some selected text. What it does is split the selected text by separate lines, and then:

If the line contains no comments, it is appended.
If the line contains some text followed by comments, it is appended with comments trimmed.
If the line starts with a comment, it does not get appended. This is in the if statement.
If the line is blank, it does not get appended. This is also in the if statement.

Here is my code:

        string[] lines = tb.SelectedText.Split('\n');
        StringBuilder sb = new StringBuilder();

        for (int i = 0; i < lines.Length; i++)
        {
            if ((lines[i].Trim() != string.Empty) || !Regex.IsMatch(lines[i], @"^\s*;(.*)$"))
            {
                if (Regex.IsMatch(lines[i], @"^(.*);(.*)$"))
                    sb.AppendLine(lines[i].Substring(0, lines[i].IndexOf(';')).Trim());
                else
                    sb.AppendLine(lines[i]);
            }
        }
        tb.SelectedText = sb.ToString();

The problem is, it isn't working as intended. Suppose if I have the following text:

test    ;test

test2   ;test

I would expect this to trim the comments and remove the blank line, but no, the blank line is STILL there. Why is this? I checked if the line was empty, so the StringBuilder shouldn't append the line if it's blank, but for some reason it does.

Also, for some reason the stringbuilder appends an extra line. How to get rid of that?

回答1:

Replace the || in the if-statement by && and use "\r\n" instead of "\n". Try this:

var lines = textBox2.SelectedText.Split(new [] {"\r\n"}, StringSplitOptions.None);
var sb = new StringBuilder();

for (int i = 0; i < lines.Length; i++)
{
    var line = lines[i].Trim();
    if ((line != string.Empty) && !Regex.IsMatch(line, @"^\s*;(.*)$"))
    {
        if (Regex.IsMatch(line, @"^(.*);(.*)$"))
            sb.AppendLine(line.Substring(0, line.IndexOf(';')).Trim());
        else
            sb.AppendLine(line);
    }
}
textBox2.SelectedText = sb.ToString();

Or with LinQ and "?:" expression:

var lines = textBox2.SelectedText .Split(new [] {"\r\n"}, StringSplitOptions.None);
var sb = new StringBuilder();

foreach (var line in lines.Select(t => t.Trim())
                          .Where(line => (line != string.Empty) && !Regex.IsMatch(line, @"^\s*;(.*)$")))
{
    sb.AppendLine(Regex.IsMatch(line, @"^(.*);(.*)$") ? line.Substring(0, line.IndexOf(';')).Trim() : line);
}
textBox2.SelectedText = sb.ToString();

回答2:

You have a problem in your logic here

if ((lines[i].Trim() != string.Empty) || !Regex.IsMatch(lines[i], @"^\s*;(.*)$")) {
    if (Regex.IsMatch(lines[i], @"^(.*);(.*)$"))
        sb.AppendLine(lines[i].Substring(0, lines[i].IndexOf(';')).Trim());
    else
        sb.AppendLine(lines[i]);
}

You enter the if when the string is not empty OR it does not match the regular expression. That means you enter it all the time, because when the first part is false (the string is empty) then the second is true (the empty string does not match your regular expression.)

Just replace the OR with an AND.

来源：https://stackoverflow.com/questions/8399213/c-sharp-removing-comments-from-a-string

标签

regex

string

.net-2.0

trim