CODEWITHSUNDEEP
c#string-comparisoncase-insensitive
Jamie
Jamie

Reputation: 2717

How can I do a case insensitive string comparison?

How can I make the line below case insensitive?

drUser["Enrolled"] = 
      (enrolledUsers.FindIndex(x => x.Username == (string)drUser["Username"]) != -1);

I was given some advice earlier today that suggested I use: 

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

the trouble is I can't get this to work, I've tried the line below, this compiles but returns the wrong results, it returns enrolled users as unenrolled and unenrolled users as enrolled.

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

Can anyone point out the problem?

Upvotes: 270

Views: 329081

Answers (9)

Ranga
Ranga

Reputation: 1401

I'd like to write an extension method for EqualsIgnoreCase

public static class StringExtensions
{
    public static bool? EqualsIgnoreCase(this string strA, string strB)
    {
        return strA?.Equals(strB, StringComparison.CurrentCultureIgnoreCase);
    }
}

Upvotes: 9

Felype
Felype

Reputation: 3136

You can (although controverse) extend System.String to provide a case insensitive comparison extension method:

public static bool CIEquals(this String a, String b) {
    return a.Equals(b, StringComparison.CurrentCultureIgnoreCase);
}

and use as such:

x.Username.CIEquals((string)drUser["Username"]);

C# allows you to create extension methods that can serve as syntax suggar in your project, quite useful I'd say.

It's not the answer and I know this question is old and solved, I just wanted to add these bits.

Upvotes: 8

TarmoPikaro
TarmoPikaro

Reputation: 5243

Others answer are totally valid here, but somehow it takes some time to type StringComparison.OrdinalIgnoreCase and also using String.Compare.

I've coded simple String extension method, where you could specify if comparison is case sensitive or case senseless with boolean, attaching whole code snippet here:

using System;

/// <summary>
/// String helpers.
/// </summary>
public static class StringExtensions
{
    /// <summary>
    /// Compares two strings, set ignoreCase to true to ignore case comparison ('A' == 'a')
    /// </summary>
    public static bool CompareTo(this string strA, string strB, bool ignoreCase)
    {
        return String.Compare(strA, strB, ignoreCase) == 0;
    }
}

After that whole comparison shortens by 10 characters approximately - compare:

Before using String extension:

String.Compare(testFilename, testToStart,true) != 0

After using String extension:

testFilename.CompareTo(testToStart, true)

Upvotes: 8

I_Al-thamary
I_Al-thamary

Reputation: 4043

I think you will find more information in this link:

http://codeidol.com/community/dotnet/controlling-case-sensitivity-when-comparing-two-st/8873/

Use the Compare static method on the String class to compare the two strings. Whether the comparison is case-insensitive is determined by the third parameter of one of its overloads. For example:

string lowerCase = "abc";
string upperCase = "AbC";
int caseInsensitiveResult = string.Compare(lowerCase, upperCase,
  StringComparison.CurrentCultureIgnoreCase);
int caseSensitiveResult = string.Compare(lowerCase,
  StringComparison.CurrentCulture);

The caseSensitiveResult value is -1 (indicating that lowerCase is "less than" upperCase) and the caseInsensitiveResult is zero (indicating that lowerCase "equals" upperCase).

Upvotes: 3

Gautam Kumar Sahu
Gautam Kumar Sahu

Reputation: 621

Please use this for comparison:

string.Equals(a, b, StringComparison.CurrentCultureIgnoreCase);

Upvotes: 42

ocean4dream
ocean4dream

Reputation: 5182

This is not the best practice in .NET framework (4 & +) to check equality 

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

Use the following instead

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

MSDN recommends:

  • Use an overload of the String.Equals method to test whether two strings are equal.
  • Use the String.Compare and String.CompareTo methods to sort strings, not to check for equality.

Upvotes: 494

user3895427
user3895427

Reputation: 65

you can always use functions: .ToLower(); .ToUpper();

convert your strings and then compare them...

Good Luck

Upvotes: -12

Oleg
Oleg

Reputation: 222007

You should use static String.Compare function like following

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

Upvotes: 37

decyclone
decyclone

Reputation: 30840

How about using StringComparison.CurrentCultureIgnoreCase instead?

Upvotes: 1

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