Why don't String.IndexOf and String.Contains agree to provide Arabic text?

Question

I want to know if I found an error in the .NET Framework or if something does not understand. After running this piece of code:

var text = "مباركُ وبعض أكثر من نص"; var word = "مبارك"; bool exist = text.Contains(word); int index = text.IndexOf(word); 

The results are "exist = true" and "index = -1"

How can it be?

Answer 1

Contains insensitive to culture:

This method performs an ordinal (case-sensitive and culture-insensitive) comparison.

IndexOf culture sensitive:

This method searches for words (case-sensitive and culture-sensitive) using the current culture.

This is the difference. If you use

 int index = text.IndexOf(word, StringComparison.Ordinal); 

then you get index 0 instead of -1 (so it matches Contains ).

No Culture Sensitive Overload Contains ; I don’t understand if IndexOf can be reliably used for this, but the CompareInfo class provides a few more options. (I really don't know much about the details of cultural comparisons, especially with the text RTL. I just know it's complicated!)