Equals s2, StringComparison. Ordinal or StringComparison. OrdinalIgnoreCase to compare as a safe default for culture independent string matching. Use to compare with StringComparison. OrdinalIgnoreCase for better performance. When the comparison is language independent for example, symbols , use a non language StringComparison. OrdinalIgnoreCase value instead of a string operation based on CultureInfo. Last: In most cases, do not use string operations based on StringComparison.
The following code example demonstrates the properties and the Create method of the StringComparer class. The example illustrates how different StringComparer objects sort three versions of the Latin letter I. NET, Ordinal. On the other hand, looks purely at the values of the raw byte s that represent the character. There's a great sample Through this blog I will show you the tricks to compare the string in C.
Usually, When people compare the two strings Don't know whether, if they are in upper case or lower case , they do it like this.. How to compare strings, The first one is the correct one, and IMHO the more efficient one, since the second 'solution' instantiates a new string instance. Equals val, "astringvalue", StringComparison. OrdinalIgnoreCase this avoids all the issues of culture-sensitive strings, but as a consequence it avoids all the issues of culture-sensitive strings.
Only you know whether that is OK in your context. Using the string. Equals static method avoids any issues with val being null. Compare "AA", "aa", StringComparison.
Compare Method String, String, Boolean. You can change this behaviour by setting a parameter when you initialize a Dictionary. In case, if we want to perform case insensitive string comparison, then we need to use OrdinalIgnoreCase property along with the Equals method.
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. Compare lowerCase, upperCase, StringComparison.
Compare lowerCase, StringComparison. CurrentCulture ;. InvariantCulture Property System. Globalization , by name by using an empty string "" in the call to a CultureInfo instantiation method. You specify the invariant culture by name by using an empty string "" in the call to a CultureInfo instantiation method. What is the Invariant Culture? The current culture can change from one user to another, The invariant culture is a special culture which is useful because it will not change.
The current culture can change from one user to another, or even from one run to another, so you can't rely on it staying the same. What does CultureInfo. However, we still recommend that you call an overload that explicitly specifies the StringComparison type even if you want to perform an ordinal comparison; this makes it easier to search code for a certain string interpretation. Be careful when you use the String. ToUpper and String. ToLower methods, because forcing a string to a uppercase or lowercase is often used as a small normalization for comparing strings regardless of case.
If so, consider using a case-insensitive comparison. The String. ToUpperInvariant and String. ToLowerInvariant methods are also available. ToUpperInvariant is the standard way to normalize case. Comparisons made using StringComparison. OrdinalIgnoreCase are behaviorally the composition of two calls: calling ToUpperInvariant on both string arguments, and doing a comparison using StringComparison.
Overloads are also available for converting to uppercase and lowercase in a specific culture, by passing a CultureInfo object that represents that culture to the method. The Char. ToUpper Char and Char. ToLower Char methods work similarly to the String.
ToLower methods described in the previous section. There is a lack of consistency in how the default overloads of these methods perform comparisons. All String. IndexOf and String. LastIndexOf methods that include a Char parameter perform an ordinal comparison, but the default String. LastIndexOf methods that include a String parameter perform a culture-sensitive comparison. If you call the String. IndexOf String or String. LastIndexOf String method and pass it a string to locate in the current instance, we recommend that you call an overload that explicitly specifies the StringComparison type.
The overloads that include a Char argument do not allow you to specify a StringComparison type. Some non-string methods that have string comparison as a central operation use the StringComparer type.
Compare methods perform the following types of string comparisons:. When you store any data in a collection, or read persisted data from a file or database into a collection, switching the current culture can invalidate the invariants in the collection. The Array. BinarySearch method assumes that the elements in the array to be searched are already sorted.
To sort any string element in the array, the Array. Sort method calls the String. Compare method to order individual elements. Using a culture-sensitive comparer can be dangerous if the culture changes between the time that the array is sorted and its contents are searched.
For example, in the following code, storage and retrieval operate on the comparer that is provided implicitly by the Thread. CurrentCulture property. If the culture can change between the calls to StoreNames and DoesNameExist , and especially if the array contents are persisted somewhere between the two method calls, the binary search may fail. A recommended variation appears in the following example, which uses the same ordinal culture-insensitive comparison method both to sort and to search the array.
The change code is reflected in the lines labeled Line A and Line B in the two examples. If this data is persisted and moved across cultures, and sorting is used to present this data to the user, you might consider using StringComparison. InvariantCulture , which operates linguistically for better user output but is unaffected by changes in culture. The following example modifies the two previous examples to use the invariant culture for sorting and searching the array.
Hashing strings provides a second example of an operation that is affected by the way in which strings are compared. The following example instantiates a Hashtable object by passing it the StringComparer object that is returned by the StringComparer. OrdinalIgnoreCase property. Because a class StringComparer that is derived from StringComparer implements the IEqualityComparer interface, its GetHashCode method is used to compute the hash code of strings in the hash table.
Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services. Privacy policy. Skip to main content. This browser is no longer supported. Download Microsoft Edge More info. Contents Exit focus mode. Best practices for comparing strings in. Note You can download the Sorting Weight Tables , a set of text files that contain information on the character weights used in sorting and comparison operations for Windows operating systems, and the Default Unicode Collation Element Table , the latest version of the sort weight table for Linux and macOS.
Important Although string comparison methods disregard embedded null characters, string search methods such as String. Is this page helpful? Yes No. Any additional feedback? Skip Submit. Submit and view feedback for This product This page. View all page feedback. Case-sensitive internal identifiers. Case-sensitive security-related settings. Case-insensitive internal identifiers. File paths. Registry keys and values.
Environment variables. Resource identifiers for example, handle names.
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