默认情况下， == 运算符对字符串如何工作？

发布于 2024-11-01 10:01:49 字数 1080 浏览 0 评论 0原文

可能的重复：
请告诉为什么在字符串的情况下，字符串对象的两个引用是相同的（下面编写的代码）

当我在 C# 中编写 s1 == s2 时，两者都声明为字符串，编译器会比较引用或内容吗？即如果 == 被 string 类覆盖？

我只是想知道为什么这段代码打印“true”：

string s1 = "hello"
string s2 = s1 + " ";
s2 = s2.Trim(); // i expect new object here
Console.WriteLine(s2 == s1);

此外，我还有一些第三方来源，其中 == 经常用于字符串比较。这让我抓狂，因为我几乎从不使用 == 来比较 Java 中的字符串，现在我无法理解这段代码是如何工作的。

C#中使用==比较字符串正常吗？

upd：感谢大家，几乎所有答案都是正确的。结论：

是的，在C#中使用“==”来比较字符串是正常的，
字符串将通过内容（而不是引用）进行比较
== 运算符对于字符串不是虚拟的。
C# 中的字符串是不可变的（这与 Java 类似）

此行为与 Java 不同，其中 String 类的“==”比较引用。

另请参阅为什么字符串不比较引用？

在我个人看来，语言不应该允许覆盖或重载 == 运算符，因为它使它像 C++ 一样困难:)

原文

Possible Duplicate:
Please tell why two references are same for string object in case of string( Code written below)

When I write in C# s1 == s2 where both declared as string would compiler compare references or content? I.e. if the == is overriden for string class?

I just wonder why this code prints "true":

string s1 = "hello"
string s2 = s1 + " ";
s2 = s2.Trim(); // i expect new object here
Console.WriteLine(s2 == s1);

Also I've some third-party sources where == is often used for strings comparision. This makes me crazy because I almost never use == to compare strings in Java and now I can't understand how this code works.

Is it normal to use == to compare strings in C#?

upd: Thanks to all, almost all answers are correct.
To conclude:

Yes, it's normal to use "==" to compare string in C#
strings will be compared by content (not reference)
== operator for strings is NOT virtual.
strings in C# are immutable (this is similar to Java)

This behavior is different to Java where "==" for String class compares references.

In my personal opinion language should not allow override or overload == operator, cause it makes it as difficult as c++ :)

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讽刺将军 2024-11-08 10:01:49

运算符不能被多态地重写，但可以被重载，字符串就是这种情况。重载检查内容是否相等（以顺序方式，没有文化敏感性）。因此，例如：

string s1 = "hello";
string s2 = (s1 + " ").Trim();

object o1 = s1;
object o2 = s2;

Console.WriteLine(s1 == s2); // True - calls overloaded ==(string, string)
Console.WriteLine(o1 == o2); // False - compares by reference

请注意这是如何在完全相同的对象上进行操作的，但是由于重载解析是在编译时执行的，因此在第二种情况下编译器不会执行重载解析。知道调用特定于字符串的运算符。

Operators can't be overridden polymorphically, but they can be overloaded which is the case for string. The overload checks for content equality (in an ordinal fashion, with no culture sensitivity). So, for example:

string s1 = "hello";
string s2 = (s1 + " ").Trim();

object o1 = s1;
object o2 = s2;

Console.WriteLine(s1 == s2); // True - calls overloaded ==(string, string)
Console.WriteLine(o1 == o2); // False - compares by reference

Note how this is operating on exactly the same objects, but because overload resolution is performed at compile-time, in the second case the compiler doesn't know to call the string-specific operator.

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