Question

I’m creating C# winforms app which has to find all occurences of a string within a file, crop the text in between, then do some processing.

The text file has following format:

—- Key_String —-

text to crop 1

—- Key_String —-

text to crop 2

—- Key_String —-

text to crop 3

Basically I’m croping "text1", "text2", "text3" from that file.

And here is the code to do the mentioned action:

string contents = "";
MatchCollection matches;
using (StreamReader reader = File.OpenText(filepath))
{
    contents = reader.ReadToEnd();
    matches = Regex.Matches(contents, "Key_String");
}
int totalmatchcount = matches.Count;

for (int i = 0; i < totalmatchcount; i++ )
{
    int indd1 = matches[i].Index;
    int indd2 = 0;
    string sub_content = "";
    if (i != totalmatchcount - 1)
    {
        indd2 = matches[i+1].Index;
        try
        {
            sub_content = contents.Substring(indd1, indd2); // error here
        }
        catch
        {
            MessageBox.Show("Index 1: "  + indd1 + "\n" +
                "Index 2: "  + indd2 + "\n" +
                "Max index (length - 1): "  + (contents.Length - 1)
                );
        }
    }
    else { sub_content = contents.Substring(indd1); }
    // do some stuff with "sub_content"
}

It works great for some of my files, however in some cases – I’m getting following error:

Index and length must refer to a location within the string.
Parameter name: length

It is very strange, because the substring that I’m cropping is located INSIDE the main string, not outside as you have guessed. I can prove it with "try-catch" output:

Index 1: 3211

Index 2: 4557

Max index (length – 1): 5869

As you can see – I’m not cropping something that is located outside the index range, so what’s the problem?

P.S. I’ve googled solutions but the basic idea in every case is – "wrong index". In my case – index is "inside" the range. Well, at least I think so.

Edit

Something similar to this should solve the problem:

 public string SubstringFix(string original, int start, int end)
    {
        int endindex = 0;
        if (end < original.Length)
        {
            endindex = end;
        }
        else
        {
            endindex = original.Length - 1;
        }

        return original.Substring(start, (end - start));
    }

Answer 1

Substring does not take two indices. It takes one index and a length. Probably, you want

indd2 - indd1

as the second parameter (and check that expression for off-by-one errors).