C#中字符串比较方法的差异 [英] Differences in string compare methods in C#

问题描述

在 C# 中比较字符串非常简单.事实上，有几种方法可以做到.我在下面的块中列出了一些.我很好奇的是它们之间的区别以及何时应该使用它们而不是其他?是否应该不惜一切代价避免?还有更多我没有列出的吗?

Comparing string in C# is pretty simple. In fact there are several ways to do it. I have listed some in the block below. What I am curious about are the differences between them and when one should be used over the others? Should one be avoided at all costs? Are there more I haven't listed?

string testString = "Test";
string anotherString = "Another";

if (testString.CompareTo(anotherString) == 0) {}
if (testString.Equals(anotherString)) {}
if (testString == anotherString) {}

(注意:我在这个例子中寻找相等，不小于或大于但也可以对此发表评论)

(Note: I am looking for equality in this example, not less than or greater than but feel free to comment on that as well)

推荐答案

以下是这些函数的工作规则:

Here are the rules for how these functions work:

stringValue.CompareTo(otherStringValue)

1. null 出现在字符串之前
2. 它使用 CultureInfo.CurrentCulture.CompareInfo.Compare，这意味着它将使用文化相关的比较.这可能意味着 ß 将等于德国的 SS 或类似的

1. null comes before a string
2. it uses CultureInfo.CurrentCulture.CompareInfo.Compare, which means it will use a culture-dependent comparison. This might mean that ß will compare equal to SS in Germany, or similar

stringValue.Equals(otherStringValue)

1. null 不等于任何东西
2. 除非您指定StringComparison 选项，否则它将使用看起来像直接序数相等性检查的内容，即ß 与SS 不同>，在任何语言或文化中

1. null is not considered equal to anything
2. unless you specify a StringComparison option, it will use what looks like a direct ordinal equality check, i.e. ß is not the same as SS, in any language or culture

stringValue == otherStringValue

1. 与 stringValue.Equals() 不同.
2. == 运算符调用静态 Equals(string a, string b) 方法(该方法又转到内部 EqualsHelper进行比较.
3. 在 null 字符串上调用 .Equals() 会得到 null 引用异常，而在 == 上会不是.

1. Is not the same as stringValue.Equals().
2. The == operator calls the static Equals(string a, string b) method (which in turn goes to an internal EqualsHelper to do the comparison.
3. Calling .Equals() on a null string gets null reference exception, while on == does not.

Object.ReferenceEquals(stringValue, otherStringValue)

只需检查引用是否相同，即它不仅仅是具有相同内容的两个字符串，而是将一个字符串对象与其自身进行比较.

Just checks that references are the same, i.e. it isn't just two strings with the same contents, you're comparing a string object with itself.

请注意，对于上面使用方法调用的选项，有更多选项的重载来指定如何比较.

Note that with the options above that use method calls, there are overloads with more options to specify how to compare.

如果您只想检查相等性，我的建议是决定是否要使用依赖于文化的比较，然后使用 .CompareTo 或 .Equals，取决于选择.

My advice if you just want to check for equality is to make up your mind whether you want to use a culture-dependent comparison or not, and then use .CompareTo or .Equals, depending on the choice.

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