C＃字符串引用类型？ [英] C# string reference type?

问题描述

我知道，串在C＃中是引用类型。这是MSDN。然而，这code没有，因为它应该再工作：

I know that "string" in C# is a reference type. This is on MSDN. However, this code doesn't work as it should then:

class Test
{
    public static void Main()
    {
        string test = "before passing";
        Console.WriteLine(test);
        TestI(test);
        Console.WriteLine(test);
    }

    public static void TestI(string test)
    {
        test = "after passing";
    }
}

输出应该是通过，因为我传递字符串作为参数，它是一个引用类型后才通过，第二个输出语句应该认识到文本在TESTI方法改变。然而，我过客使它看起来它是按值传递的不是裁判前才通过搞定。据我所知，字符串是不可变的，但我看不出这将解释是怎么回事。我在想什么？谢谢你。

The output should be "before passing" "after passing" since I'm passing the string as a parameter and it being a reference type, the second output statement should recognize that the text changed in the TestI method. However, I get "before passing" "before passing" making it seem that it is passed by value not by ref. I understand that strings are immutable, but I don't see how that would explain what is going on here. What am I missing? Thanks.

推荐答案

到字符串的参考是按值传递。有路过的价值的参考和引用传递对象之间有很大的区别。这是不幸的单词参考，在这两种情况下被使用。

The reference to the string is passed by value. There's a big difference between passing a reference by value and passing an object by reference. It's unfortunate that the word "reference" is used in both cases.

如果您的做的传递字符串引用的按的参考，它会像您期望的工作：

If you do pass the string reference by reference, it will work as you expect:

using System;

class Test
{
    public static void Main()
    {
        string test = "before passing";
        Console.WriteLine(test);
        TestI(ref test);
        Console.WriteLine(test);
    }

    public static void TestI(ref string test)
    {
        test = "after passing";
    }
}

现在需要进行更改其一个参考指的是对象，使得改变到变量（例如作为一个参数），以让它指向一个不同的对象之间进行区分。我们无法更改为字符串，因为字符串是不可变的，但我们可以证明它的StringBuilder 而不是：

Now you need to distinguish between making changes to the object which a reference refers to, and making a change to a variable (such as a parameter) to let it refer to a different object. We can't make changes to a string because strings are immutable, but we can demonstrate it with a StringBuilder instead:

using System;
using System.Text;

class Test
{
    public static void Main()
    {
        StringBuilder test = new StringBuilder();
        Console.WriteLine(test);
        TestI(test);
        Console.WriteLine(test);
    }

    public static void TestI(StringBuilder test)
    {
        // Note that we're not changing the value
        // of the "test" parameter - we're changing
        // the data in the object it's referring to
        test.Append("changing");
    }
}

请参阅我的文章参数传递了解更多详情。

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