保证字符串不变时，字符串比较是否会因文化而异？ [英] Could string comparisons really differ based on culture when the string is guaranteed not to change?

问题描述

我正在从配置文件中读取加密的凭据/连接字符串。 Resharper告诉我，此行上的 String.IndexOf（string）在这里是特定于文化的：

I'm reading encrypted credentials/connection strings from a config file. Resharper tells me, "String.IndexOf(string) is culture-specific here" on this line:

if (line.Contains("host=")) {
    _host = line.Substring(line.IndexOf(
        "host=") + "host=".Length, line.Length - "host=".Length);

...因此要将其更改为：

...and so wants to change it to:

if (line.Contains("host=")) {
    _host = line.Substring(line.IndexOf("host=", System.StringComparison.Ordinal) + "host=".Length, line.Length -   "host=".Length);

无论应用程序可能部署在哪里，我正在读取的值始终为 host = 。添加此 System.StringComparison.Ordinal位真的明智吗？

The value I'm reading will always be "host=" regardless of where the app may be deployed. Is it really sensible to add this "System.StringComparison.Ordinal" bit?

更重要的是，它会伤害任何东西（使用它）吗？

More importantly, could it hurt anything (to use it)?

推荐答案

绝对。每个MSDN（ http://msdn.microsoft.com/en-us/library/ d93tkzah.aspx ），

Absolutely. Per MSDN (http://msdn.microsoft.com/en-us/library/d93tkzah.aspx),

此方法执行一个单词（区分大小写的和区分文化的 >）
使用当前区域性进行搜索。

This method performs a word (case-sensitive and culture-sensitive) search using the current culture.

因此，如果您在不同区域性下运行它，可能会得到不同的结果（通过控制面板中的区域和语言设置）。

So you may get different results if you run it under a different culture (via regional and language settings in Control Panel).

在这种情况下，您可能不会遇到问题，但会抛出 i 在搜索字符串中运行并在土耳其运行，这可能会破坏您的一天。

In this particular case, you probably won't have a problem, but throw an i in the search string and run it in Turkey and it will probably ruin your day.

请参见MSDN： http://msdn.microsoft.com/en-us/library/ms973919.aspx

这些新的建议和API的存在是为了减轻有关默认字符串API行为的误导性假设。出现
的错误的典型示例是 Turkish-I问题，该错误中的非语言字符串数据是用语言解释的
。

These new recommendations and APIs exist to alleviate misguided assumptions about the behavior of default string APIs. The canonical example of bugs emerging where non-linguistic string data is interpreted linguistically is the "Turkish-I" problem.

几乎所有拉丁字母，包括美国英语，字符
i（\u0069）是字符I（\u0049）的小写版本。这种
大小写规则很快成为使用
这种文化进行编程的人的默认设置。但是，在土耳其语（ tr-TR）中，存在大写字母
i带点（，u0130），它是
i的大写形式。同样，在土耳其语中，有一个小写的 i无点或
（\u0131），将大写为I。在Azeri
文化（ az）中也发生这种情况

For nearly all Latin alphabets, including U.S. English, the character i (\u0069) is the lowercase version of the character I (\u0049). This casing rule quickly becomes the default for someone programming in such a culture. However, in Turkish ("tr-TR"), there exists a capital "i with a dot," character (\u0130), which is the capital version of i. Similarly, in Turkish, there is a lowercase "i without a dot," or (\u0131), which capitalizes to I. This behavior occurs in the Azeri culture ("az") as well.

因此，通常关于资本化i或小写字母
的假设在所有文化中均无效。如果使用默认的
重载用于字符串比较例程，则它们将是
，这取决于区域性之间的差异。对于非语言数据，如以下示例中的
一样，这会产生不希望的结果：

Therefore, assumptions normally made about capitalizing i or lowercasing I are not valid among all cultures. If the default overloads for string comparison routines are used, they will be subject to variance between cultures. For non-linguistic data, as in the following example, this can produce undesired results:

    Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US")
Console.WriteLine("Culture = {0}",
   Thread.CurrentThread.CurrentCulture.DisplayName);
Console.WriteLine("(file == FILE) = {0}", 
   (String.Compare("file", "FILE", true) == 0));

Thread.CurrentThread.CurrentCulture = new CultureInfo("tr-TR");
Console.WriteLine("Culture = {0}",
   Thread.CurrentThread.CurrentCulture.DisplayName);
Console.WriteLine("(file == FILE) = {0}", 
   (String.Compare("file", "FILE", true) == 0));

由于比较I的差异，$的结果当线程区域性更改时，b $ b比较也会更改。这是
的输出：

Because of the difference of the comparison of I, results of the comparisons change when the thread culture is changed. This is the output:

Culture = English (United States)
(file == FILE) = True
Culture = Turkish (Turkey)
(file == FILE) = False

这里是一个没有大小写的示例：

Here is an example without case:

var s1 = "é"; //é as one character (ALT+0233)
var s2 = "é"; //'e', plus combining acute accent U+301 (two characters)

Console.WriteLine(s1.IndexOf(s2, StringComparison.Ordinal)); //-1
Console.WriteLine(s1.IndexOf(s2, StringComparison.InvariantCulture)); //0
Console.WriteLine(s1.IndexOf(s2, StringComparison.CurrentCulture)); //0

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