String comparison InvariantCultureIgnoreCase vs OrdinalIgnoreCase

Question

Which would be better code   int index   fileName LastIndexOf      StringComparison InvariantCultureIgnoreCase     or  int index   fileName LastIndexOf      StringComparison OrdinalIgnoreCase

User · Accepted Answer

If you really want to match only the dot, then StringComparison.Ordinal would be fastest, as there is no case-difference.

"Ordinal" doesn't use culture and/or casing rules that are not applicable anyway on a symbol like a ..

User · Answer

Neither code is always better  They do different things  so they are good at different things   InvariantCultureIgnoreCase uses comparison rules based on english  but without any regional variations  This is good for a neutral comparison that still takes into account some linguistic aspects   OrdinalIgnoreCase compares the character codes without cultural aspects  This is good for exact comparisons  like login names  but not for sorting strings with unusual characters like    or     This is also faster because there are no extra rules to apply before comparing

User · Answer

You seem to be doing file name comparisons  so I would just add that OrdinalIgnoreCase is closest to what NTFS does  it s not exactly the same  but it s closer than InvariantCultureIgnoreCase

User · Answer

FXCop typically prefers OrdinalIgnoreCase   But your requirements may vary   For English there is very little difference  It is when you wander into languages that have different written language constructs that this becomes an issue  I am not experienced enough to give you more than that   OrdinalIgnoreCase     The StringComparer returned by the    OrdinalIgnoreCase property treats    the characters in the strings to   compare as if they were converted   to uppercase using the conventions   of the invariant culture  and then   performs a simple byte comparison   that is independent of language    This is most appropriate when   comparing strings that are generated   programmatically or when comparing   case-insensitive resources such as   paths and filenames    http   msdn microsoft com en-us library system stringcomparer ordinalignorecase aspx   InvariantCultureIgnoreCase     The StringComparer returned by the   InvariantCultureIgnoreCase property   compares strings in a linguistically   relevant manner that ignores case  but   it is not suitable for display in any   particular culture  Its major   application is to order strings in a   way that will be identical across   cultures    http   msdn microsoft com en-us library system stringcomparer invariantcultureignorecase aspx      The invariant culture is the   CultureInfo object returned by the   InvariantCulture property       The InvariantCultureIgnoreCase   property actually returns an instance   of an anonymous class derived from the   StringComparer class

[c#] String comparison: InvariantCultureIgnoreCase vs OrdinalIgnoreCase?

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