在c#中通过ref关键字调用类对象[重复]

Posted 2023-02-25

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【中文标题】在c#中通过ref关键字调用类对象[重复]【英文标题】：Call class object by ref keyword in c# [duplicate] 【发布时间】：2014-11-15 09:06:55 【问题描述】：

public class Test

    public string Name;

    public void CallFunctionByObjectRef(Test a)
    
        a.Name = "BCD";
        a = null;
    

    public void CallFunctionByObjectRefTORef(ref Test a)
    
        a.Name = "BCD";
        a = null;
    


class Program

    static void Main(string[] args)
    

        Test test = new Test();
        test.Name = "ABC";
        test.CallFunctionByObjectRef(test);


        Test test1 = new Test();
        test1.Name = "ABC";
        test1.CallFunctionByObjectRefTORef(ref test1);

        Console.WriteLine(test.Name);
        Console.WriteLine(test1.Name);
        Console.Read();

上面调用了两个函数（使用 ref 关键字，通过对象传递）。我从他们那里得到不同的输出。但是默认情况下类对象通过引用传递，为什么我得到不同的输出。

【问题讨论】：

不。默认情况下，参数始终按值传递。问题是，对于引用类型，被复制和传递的值就是引用。输出结果是什么？这里有一篇关于该主题的精彩文章 - yoda.arachsys.com/csharp/parameters.html @mdebeus：应该是BCD，后跟System.NullReferenceException。 @Timothy - ABISHEK 仍应在问题中说明这一点。 【参考方案1】：

在您的情况下，对类对象的引用是按值传递的。

给定变量a 的值或引用类型和接受a 作为值或引用的方法：

class A 
// or
struct A 

var a = new A();

Foo(ref a);
// or
Foo(a);

你可以：

按值传递引用类型：您可以更改变量引用的对象，但不能更改变量本身。按引用传递引用类型：可以更改变量引用的对象，也可以更改变量本身。按值传递值类型：不能更改变量引用的对象，也不能更改变量本身。通过引用传递值类型：你可以改变变量引用的对象，你不能改变变量本身。

【讨论】：

【参考方案2】：

 /* Here you are passing pointer to the variable. For example variable test has got memory address
             * 0X200001.
             * When you pass test, you are saying that there are two variables that points to 0X200001 (one in main and another in CallFunctionByObjectRef i.e. variable a)
             * Thus when you are changing the value for a variable to null, you are changing the direction to link with null memory location.
             * 
             * It is called  reference.
             * When you came back to Main, test variable is still pointing to the memory 0X200001
            */
            Test test = new Test();
            test.Name = "ABC";

            test.CallFunctionByObjectRef(test);

            /*
            * In this case you are saying that create a variable test1 that gives a memory as: 0X200002
            * Then you are passing a pointer to pointer i.e. you are sending an actual test1 variable. 
             * so whatever you will change here will get impacted in Main.
            */
            Test test1 = new Test();
            test1.Name = "ABC";

            test1.CallFunctionByObjectRefTORef(ref test1);

            Console.WriteLine(test.Name);
            Console.WriteLine(test1.Name);
            Console.Read();

如果你想了解更多，那么你需要从 C/c++ 指针编程中获得一个想法，并搜索“Reference to a Pointer”

【讨论】：

谢谢，我喜欢你的回答【参考方案3】：

阅读Passing Reference-Type Parameters (MSDN)