Difference between InvariantCulture and Ordinal string comparison

当比较c＃中的两个字符串是否相等时，InvariantCulture和Ordinal比较有什么区别？

---

InvariantCulture

Uses a "standard" set of character orderings (a,b,c, ... etc.). This is in contrast to some specific locales, which may sort characters in different orders ('a-with-acute' may be before or after 'a', depending on the locale, and so on).

Ordinal

On the other hand, looks purely at the values of the raw byte(s) that represent the character.

---

There's a great sample at http://msdn.microsoft.com/en-us/library/e6883c06.aspx that shows the results of the various StringComparison values. All the way at the end, it shows (excerpted):

StringComparison.InvariantCulture:
LATIN SMALL LETTER I (U+0069) is less than LATIN SMALL LETTER DOTLESS I (U+0131)
LATIN SMALL LETTER I (U+0069) is less than LATIN CAPITAL LETTER I (U+0049)
LATIN SMALL LETTER DOTLESS I (U+0131) is greater than LATIN CAPITAL LETTER I (U+0049)

StringComparison.Ordinal:
LATIN SMALL LETTER I (U+0069) is less than LATIN SMALL LETTER DOTLESS I (U+0131)
LATIN SMALL LETTER I (U+0069) is greater than LATIN CAPITAL LETTER I (U+0049)
LATIN SMALL LETTER DOTLESS I (U+0131) is greater than LATIN CAPITAL LETTER I (U+0049)

You can see that where InvariantCulture yields (U+0069, U+0049, U+00131), Ordinal yields (U+0049, U+0069, U+00131).

---

It does matter, for example - there is a thing called character expansion

        var s1 = "Strasse";
        var s2 = "Straße";

        s1.Equals(s2, StringComparison.Ordinal);           //false

        s1.Equals(s2, StringComparison.InvariantCulture);  //true

With InvariantCulture the ß character gets expanded to ss.

---

Pointing to Best Practices for Using Strings in the .NET Framework:

Use StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase for comparisons as your safe default for culture-agnostic string matching.

Use comparisons with StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase for better performance.

Use the non-linguistic StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase values instead of string operations based on CultureInfo.InvariantCulture when the comparison is linguistically irrelevant (symbolic, for example).

And finally:

Do not use string operations based on StringComparison.InvariantCulture in most cases . One of the few exceptions is when you are persisting linguistically meaningful but culturally agnostic data.

链接地址: http://www.djcxy.com/p/21188.html

上一篇: Html.Partial与Html.RenderPartial＆Html.Action与Html.RenderAction

下一篇: 不变文化与序数字符串比较的区别