Cut the string to be <= 80 characters AND must keep the words without cutting them

Question

I am new to C#, but I have a requirement to cut the strings to be <= 80 characters AND they must keep the words integrity (without cutting them)

Examples

Before: I have a requirenment to cut the strings to be <= 80 characters AND must keep the words without cutting them (length=108)
After: I have a requirenment to cut the strings to be <= 80 characters AND must keep (length=77)

Before: requirenment to cut the strings to be <= 80 characters AND must keep the words without cutting them (length=99)
After: requirenment to cut the strings to be <= 80 characters AND must keep the words (length=78)

Before: I have a requirenment the strings to be <= 80 characters AND must keep the words without cutting them (length=101)
After: I have a requirenment the strings to be <= 80 characters AND must keep the words (length=80)

I want to use the RegEx, but I don't know anything about the regex. It would be a hassle to to the else-if's for this. I would appreciate if you could point me to the right article which I could use to create this expression.

this is my function that I want to cut to one line:

public String cutTitleto80(String s){
    String[] words = Regex.Split(s, "\\s+");
    String finalResult = "";
    foreach (String word in words)
    {
        String tmp = finalResult + " " + word;
        if (tmp.Length > 80)
        {
            return finalResult;
        }
        finalResult = tmp;
    }
    return finalResult;
}

Answer 1

Try

^(.{0,80})(?: |$)

This is a capturing greedy match which must be followed by a space or end of string. You could also use a zero-width lookahead assertion, as in

^.{0,80}(?= |$)

If you use a live test tool like http://regexhero.net/tester/ it's pretty cool, you can actually see it jump back to the word boundary as you type beyond 80 characters.

And here's one which will simply truncate at the 80th character if there are no word boundaries (spaces) to be found:

^(.{1,80}(?: |$)|.{80})

Answer 2

Here's an approach without using Regex: just split the string (however you'd like) into whatever you consider "words" to be. Then, just start concatenating them together using a StringBuilder , checking for your desired length, until you can't add the next "word". Then, just return the string that you have built up so far.

(Untested code ahead)

public string TruncateWithPreservation(string s, int len)
{
    string[] parts = s.Split(' ');
    StringBuilder sb = new StringBuilder();

    foreach (string part in parts)
    {
        if (sb.Length + part.Length > len)
            break;

        sb.Append(' ');
        sb.Append(part);
    }

    return sb.ToString();
}

Answer 3

string truncatedText = text.Substring(0, 80);  // truncate to 80 characters
if (text[80] != ' ')  // don't remove last word if a space occurs after it in the original string (in other words, last word is already complete)
    truncatedText = truncatedText.Substring(0, truncatedText.LastIndexOf(' '));  // remove any cut-off words

Updated to fix issue from comments where last word could get cut off even if it is complete.

Answer 4

This isn't using regex but this is how I would do it:

Use String.LastIndexOf to get the last space before the 81st char.
If the 81th char is a space then take it until 80.
if it returns a number > -1 cut it off there.
If it's -1 you-have-a-really-long-word-or-someone-messing-with-the-system so you do wathever you like.