CODEWITHSUNDEEP
c#stringsubstring
tequilaras
tequilaras

Reputation: 279

C# take a substring of a string

I am taking a line from a file only if that file doen't have a specific pattern.. and i want to take from that line the last 3 chars... my code is:

        while (!line.Contains(pattern))
        {
             String num = line.Substring((line.Length - 3), (line.Length - 2));
             System.Console.WriteLine(num);
        }

but i get an error..

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

why i get that? i am starting the new string 3 chars before the end of the line and i stop 2 chars before.. :\

Upvotes: 5

Views: 2790

Answers (6)

Jacob Sobus
Jacob Sobus

Reputation: 981

The problem is that you try to get more characters then your array have.

Extensions are best for problems like this one ;) Mine have some dirty name but everyone know what it would do - this is exception safe substring:

public static string SubstringNoLongerThenSource(this string source, int startIndex, int maxLength)
{
    return source.Substring(startIndex, Math.Min(source.Length - startIndex, maxLength));
}

So in your exact problem it should be like that:

String num = line.SubstringNoLongerThenSource((line.Length - 3), 3);
System.Console.WriteLine(num);

So num will have max 3 letters if the string you provide to function have enough letters :)

Upvotes: 1

Digbyswift
Digbyswift

Reputation: 10410

This is happening because the last parameter of Substring() should be the length of the string to extract.

In your case it should be 3

, and not line.Length - 2

The first parameter should also be:

line.Length - 3

Upvotes: -1

BLUEPIXY
BLUEPIXY

Reputation: 40155

String num = line.Substring(line.Length - 3)

Upvotes: 0

FailedDev
FailedDev

Reputation: 26940

This is dangerous. What if the length of the line is < 3? You should probably check this otherwise you will get an exception.

In addition you should use the substring method as depicted here : 

String num = line.Substring((line.Length - 3), 3);

Upvotes: 1

rotman
rotman

Reputation: 1651

Second argument of Substring is how many chars it have to take starting from first argument. It should just look like that: String num = line.Substring(line.Length - 3, 3);

Upvotes: 2

Mike Christensen
Mike Christensen

Reputation: 91726

Substring takes an offset and then a number of characters to return:

http://msdn.microsoft.com/en-us/library/aa904308%28v=VS.71%29.aspx

So:

String num = line.Substring((line.Length - 3), 3);

This of course assumes that line.Length > 3. You could check with:

String num = (line.Length < 3) ? line : line.Substring((line.Length - 3), 3);

Upvotes: 9

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