保证字符串不变时，字符串比较是否会因文化而异？

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（），

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

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：

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));

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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