c sharp programming

String equality comparison


Despite ordinal’s  limitations,  string’s  == operator  always performs  ordinal  case-
sensitive comparison. The same goes for the instance version of string.Equals when
called without arguments; this defines the “default” equality comparison behavior
for the string type.
The ordinal algorithm was chosen  for string’s == and Equals
functions because  it’s both highly  efficient  and  deterministic.
String  equality  comparison  is  considered  fundamental  and  is
performed far more frequently than order comparison.
A “strict” notion of equality is also consistent with the general
use of the == operator.


The following methods allow culture-aware or case-insensitive comparisons:
public bool Equals(string value, StringComparison comparisonType);
public static bool Equals (string a, string b,
                           StringComparison comparisonType);
The static version is advantageous in that it still works if one or both of the strings
are null. StringComparison is an enum defined as follows:


The static version is advantageous in that it still works if one or both of the strings
are null. StringComparison is an enum defined as follows:
public enum StringComparison
{
  CurrentCulture,               // Case-sensitive
  CurrentCultureIgnoreCase,
  InvariantCulture,             // Case-sensitive
  InvariantCultureIgnoreCase,
  Ordinal,                      // Case-sensitive
  OrdinalIgnoreCase
}


For example:
Console.WriteLine (string.Equals ("foo", "FOO",
                   StringComparison.OrdinalIgnoreCase));   // True
Console.WriteLine ("?" == "u");                            // False
Console.WriteLine (string.Equals ("?", "u",
                   StringComparison.CurrentCulture));      // ?
(The result of the final comparison is determined by the computer’s current language
settings.)