Substring Length cannot be less than zero

Question

I'm separating a string by first name and last name.

I equate the last word to the last name. I equate the remainder to the firstname.

This string can be empty or null. I'm checking for null return.

but in case the string is empty I get the following error.

or I get an error when only the name. for example; string test = "Jack";

How can I do this in a single line without adding another "if else" control to the code?

https://dotnetfiddle.net/7lr07G

[System.ArgumentOutOfRangeException: Length cannot be less than zero.
Parameter name: length]
   at System.String.Substring(Int32 startIndex, Int32 length)

Answer 1

The problem is test.LastIndexOf(" ") which returns -1 if there is no space in test. Have a look at MSDN - String.Substring

You can use String.Contains

var firstname = !string.IsNullOrEmpty(test) && test.Contains(" ") 
        ? test.Substring(0, test.LastIndexOf(" ")) 
        : string.IsNullOrEmpty(test) ? string.Empty : test;
var lastname = !string.IsNullOrEmpty(test) && test.Contains(" ") 
        ? test.Split(' ').Last() 
        : string.Empty;

to check if there is a space in test.

I recommend using String.IsNullOrEmpty instead of test != null.

Answer 2

Try with this:

    //string test = "Jack ";
    //string test = "Jack";
    string test = "Jack Nelsson";
    var firstname = string.Empty;
    var lastname =  string.Empty;

    if (!string.IsNullOrEmpty(test))
    {
        var index =  test.LastIndexOf(" ");
        if (index < 0 || index >= test.Length - 1)
        {
            firstname = test.TrimEnd();
        }
        else
        {
            firstname = test.Substring(0, index);
            lastname =  test.Substring(index + 1);
        }
    }
    Console.WriteLine(firstname);
    Console.WriteLine(lastname);

By default, we set string.Empty. If test has a string, we search last whitespace and store in a variable to use later.

If no namespace found: set firstname to all text. If whitespace found at the end of the string: set firstname to all text without ending spaces. We need to check this case because substring with index+1 fail in this case. In other case, split the string in that point.

Answer 3

I prefer to use IndexOf as little as possible, because I always end up confusing myself with the indices. So here's different approach:

string firstname = "";
string lastname = "";
if (!string.IsNullOrEmpty(name))
{
    var parts = name.Split(' ');
    lastname = parts[parts.Length-1];
    firstname = string.Join(" ", parts.Take(parts.Length-1));
}

It simply splits using space, then makes the last part the last name and join the others as the first name.

EDIT I just saw Mighty Badaboom's solution and was inspired by the use of Last. Here's a version with even fewer integers involved:

string firstname = "";
string lastname = "";
if (!string.IsNullOrEmpty(name))
{
    var parts = name.Split(' ');
    lastname = parts.Last();
    firstname = string.Join(" ", parts.SkipLast(1));
}

SkipLast requires .NET standard 2.1. If on older standard you can go for:

    firstname = string.Join(" ", parts.Reverse().Skip(1).Reverse());

Answer 4

Try this one:

string test = "Jack Daniels";
    
    var firstname = string.IsNullOrEmpty(test)
        ? string.Empty
        : (test.Contains(" ") ? (test.Substring(0, test.LastIndexOf(" "))).Trim() : test);
    var lastname = string.IsNullOrEmpty(test)
        ? string.Empty
        : (test.Contains(" ") ? (test.Substring(test.LastIndexOf(" ")).Trim()) : string.Empty);
    
    Console.WriteLine("firstname>>" + firstname);
    Console.WriteLine("lastname>>" + lastname);