Substring excluding two strings c# return an error

Question

I'm trying to extract a portion of the string,I use two patterns, the string I'm interested in is in the middle of these two pattern...But I get this error ... where did I fail?

[System.ArgumentOutOfRangeException: Index and length must refer to a location within the string. Parameter name: length] at System.String.Substring(Int32 startIndex, Int32 length) at Program.Main() :line 16

This is the code

using System;
using System.Text.RegularExpressions;

public class Program
{
    public static void Main()
    {
        string pattern = @"<Code>";
        string _pattern = @"</Code>";
        Regex regex = new Regex(pattern);
        Regex _regex = new Regex(_pattern);
        string str = "<?xml version=\"1.0\" encoding=\"UTF-16\" ?><Codici QuoteParams><Code>AC-ALTRE-SPESE-T</Code></Codici QuoteParams>";

        var matches = regex.Matches(str);
        var _matches = _regex.Matches(str);
        string firstString = str.Substring(0+str.IndexOf(matches[0].ToString()),str.IndexOf(_matches[0].ToString()));
        Console.WriteLine(firstString);

    }
}

It means that you have addressed something that doesn't exist. For example, you have a list with 5 items in it, and you ask for the 6th, or you have a 5 character string, and ask for the 6th. Personally, I'd advocate using the XmlSerializer to deserialize the XML, or XmlDocument to parse it, rather than using regex. — ProgrammingLlama, Jan 29 '20 at 08:32
Not sure what the problem is, but I'm fairly sure [you should be using an XML parser](https://stackoverflow.com/a/1732454/106159) to parse it! — Matthew Watson, Jan 29 '20 at 08:33
IF you have XML document, then use proper tools for that, such as `XDocument` class or `XmlDocument`. — Michał Turczyn, Jan 29 '20 at 08:37

germi · Answer 1 · 2020-01-29T08:41:30.497

String.Substring does not take start and end index, but start index and length.

The usual approach therefore is to get the start index and then calculate the length like this:

var start = myString.IndexOf(firstPart);
var end = myString.IndexOf(lastPart);
var length = end - start;
var substring = myString.Substring(start, length);

For this specific case though I would suggest you use the usual XML functionality in C# like XDocument which is more robust than using regex for this.

score 1 · Answer 2 · answered Jan 29 '20 at 08:45

1

Alternatively, you can use this Regex pattern to match and capture the code:

string code = Regex.Match(str, "(?<=<Code>).*(?=</Code>)").Value;

You can try it out Here

answered Jan 29 '20 at 08:45

Innat3

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Substring excluding two strings c# return an error

2 Answers2