How to Perform Case-Insensitive String Comparisons Correctly in C#?

Case-insensitive string comparison in C#

When doing string comparisons in C#, you usually need to ignore case. While you might initially consider using the StringComparison.OrdinalIgnoreCase method with Equals, this may lead to unexpected results.

In the following code example:

drUser["Enrolled"] = 
      (enrolledUsers.FindIndex(x => x.Username.Equals((string)drUser["Username"], 
                                 StringComparison.OrdinalIgnoreCase)));

The problem is using the Equals method with an expression lambda. The expression lambda expects a boolean expression, but the Equals method returns void.

In .NET Framework 4 and above, it is recommended to use the String.Compare method combined with StringComparison.OrdinalIgnoreCase for case-insensitive string comparison, as shown below:

String.Compare(x.Username, (string)drUser["Username"], 
                  StringComparison.OrdinalIgnoreCase) == 0

Alternatively, to make the code more readable and less error-prone, you can use the String.Equals method, like this:

String.Equals(x.Username, (string)drUser["Username"], 
                   StringComparison.OrdinalIgnoreCase) 

These methods ensure that string comparisons are performed in a case-insensitive manner, providing accurate results.

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