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CompareInfo class

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This article provides supplementary remarks to the reference documentation for this API.

Conventions for comparing and sorting data vary from culture to culture. For example, sort order may be based on phonetics or on the visual representation of characters. In East Asian languages, characters are sorted by the stroke and radical of ideographs. Sorting also depends on the order languages and cultures use for the alphabet. For example, the Danish language has an "Æ" character that it sorts after "Z" in the alphabet. In addition, comparisons may be case-sensitive or case-insensitive, and casing rules may also differ by culture. The CompareInfo class is responsible for maintaining this culture-sensitive string comparison data and for performing culture-sensitive string operations.

Typically, you do not have to instantiate a CompareInfo object directly, because one is used implicitly by all non-ordinal string comparison operations, including calls to the String.Compare method. However, if you do want to retrieve a CompareInfo object, you can do it in one of these ways:

Ignored search values

Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. Comparison methods such as IndexOf and LastIndexOf do not consider such characters when they perform a culture-sensitive comparison. Ignorable characters include:

  • String.Empty. Culture-sensitive comparison methods will always find an empty string at the beginning (index zero) of the string being searched.

  • A character or string consisting of characters with code points that are not considered in the operation because of comparison options, In particular, the CompareOptions.IgnoreNonSpace and CompareOptions.IgnoreSymbols options produce searches in which symbols and nonspacing combining characters are ignored.

  • A string with code points that have no linguistic significance. For example, a soft hyphen (U+00AD) is always ignored in a culture-sensitive string comparison.

Security considerations

If a security decision depends on a string comparison or a case change, you should use the InvariantCulture property to ensure that the behavior is consistent, regardless of the culture settings of the operating system.

Note

When possible, you should use string comparison methods that have a parameter of type CompareOptions to specify the kind of comparison expected. As a general rule, use linguistic options (using the current culture) for comparing strings displayed in the user interface and specify Ordinal or OrdinalIgnoreCase for security comparisons.