C# String Comparison Explained

When doing string comparisons, I always defaulted to StringComparison.InvariantCultureIgnoreCase without giving it much further thought.

However, I recently had to explain what it actually did (and what it doesn’t) and I was a bit at a loss. This is what I found out.

Understanding how to compare strings properly is crucial, especially when dealing with internationalization and localization. C# offers several methods for comparing strings, each tailored to specific needs and scenarios. In this blog post, we’ll explore the nuances of CurrentCulture, CurrentCultureIgnoreCase, InvariantCulture, InvariantCultureIgnoreCase, Ordinal, and OrdinalIgnoreCase comparisons through practical examples.

The Basics of String Comparison in C#

String comparison in C# can be done using several approaches, each serving different purposes:

• Culture-Sensitive Comparisons: CurrentCulture and InvariantCulture comparisons consider linguistic rules of a specific culture, which is essential for displaying data in a way that is familiar to the user.
• Case-Insensitive Comparisons: Adding IgnoreCase to CurrentCulture or InvariantCulture makes the comparison case-insensitive, which is useful when the case should not affect the comparison outcome.
• Ordinal Comparisons: Ordinal and OrdinalIgnoreCase comparisons are based on the binary values of characters, making them suitable for internal, non-user-facing operations where performance is critical.

Examples

Example 1: The German “Straße” and Culture-Sensitive Comparison

When comparing “straße” (street in German) to “strasse”, the differences between comparison methods become evident:

• CurrentCulture (de-DE): Considers them equal because it applies German linguistic rules where ‘ß’ and ‘ss’ are considered equal.
• InvariantCulture: Sees them as different, as it doesn’t apply specific cultural rules.
• Ordinal: Also finds them different, purely based on binary character values.

Example 2: French Accented Characters and Culture-Sensitive Comparison

By contrast, in French accents are important so comparing “côte” with “cote” is always different:

• CurrentCulture (fr-FR): Treats them as different due to the distinct linguistic importance of accents in French.
• InvariantCulture & OrdinalIgnoreCase: Still considers them different, emphasizing the binary difference without cultural context.

Conclusion

These examples underscore the importance of choosing the right string comparison method:

• User-Facing Content: Use culture-sensitive comparisons (CurrentCulture or CurrentCultureIgnoreCase) to respect the linguistic rules and user expectations based on their locale.
• Data Storage and Internal Logic: Opt for InvariantCulture or Ordinal comparisons for consistency across cultures, ensuring that your application’s behavior doesn’t change unexpectedly when deployed in different locales.
• Performance Considerations: Ordinal comparisons are faster than culture-sensitive ones, making them the preferred choice for operations where performance is critical and cultural nuances are not a concern.