Are there other functions that can result in "StartIndex cannot be less than zero"?

Question

We have a customer who is reported receiving an error message along the lines of "StartIndex cannot be less than zero. Parameter name: startIndex". This is a standard error message usually thrown in the Substring and Remove functions of the String class. Unfortunately, I am unable to get ahold of the data that this is failing on for them, so I'm forced to debug this by looking at the source code.

I have looked for all incidences of Substring and Remove and verified that their StartIndex parameter could not be less than 0. I searched for all uses of "startIndex" and verified that, in the two cases where they were being used as the first parameter of a string function, it could not mathematically be less than 0 (in both cases, it was given the return value of an IndexOf function, but then a string Length and the value of 2 were added to it, so 1 is the smallest value it could have).

This suggests to me that either this is an issue which was fixed in prior codebases, they have a nonstandard codebase, or I'm looking in the wrong place. Are there any other functions in C# that raise this sort of error text? Or is there any way in which it could be reporting the wrong input parameter? Am I just misunderstanding this error message?

Answer 1

Here's 91 methods from System.dll and mscorlib.dll:

static class Program
{
    static void Main()
    {
        var names =
            GetMethodsWithParameter(typeof(object), "startIndex")
            .Concat(GetMethodsWithParameter(typeof(Uri), "startIndex"))
        .Distinct();
        foreach(var name in names)
        {
            Console.WriteLine(name);
        }
    }

    private static IEnumerable<string> GetMethodsWithParameter(Type assemblyOrigin, string name)
    {
        foreach(var type in assemblyOrigin.Assembly.GetTypes())
        {
            foreach(var method in type.GetMethods(
                BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static))
            {
                if(method.GetParameters().Any(x => x.Name == name))
                {
                    yield return type.FullName + "." + method.Name;
                }
            }
        }
    }
}

Answer 2

There is more than just Substring and Remove with startIndex parameter:

• String.IndexOf / String.LastIndexOf
• String.IndexOfAny / String.LastIndexOfAny
• String.Join
• String.ToCharArray

Most of above with several overloads which contain startIndex parameter.

You should definitely get a call stack, otherwise it will be really hard to find place where problem occurs.