C# - String IndexOf method with second argument equal to String length

Question

At some point in my code, I use this method:

IndexOf(string str, int startIndex)

I am also doing some calculations before, and I invoke this method with second argument (startIndex) equal to length of a string passed as first argument. Of course, no such an index exists in a string, and if we did something like this:

string[string.Length] 

we would get an IndexOutOfRangeException

How does that method work exactly? In MSDN documentation it is clearly said, that startIndex is zero-based index of a string. Does it work and doesn't throw because a char array that String class operates on is null-terminated? I want to make sure that my program won't throw at any point.

Answer 1

It's mentioned explicitly in the documentation:

Index numbering starts from 0. The startIndex parameter can range from 0 to the length of the string instance. If startIndex equals the length of the string instance, the method returns -1.