C＃变量范围

问题描述

请考虑以下示例：

using Microsoft.VisualStudio.TestTools.UnitTesting;
using System.Diagnostics;

namespace ArrayTest
{
    [TestClass]
    public class UnitTest1
    {
        class TestClass
        {
            public byte[] arr = null;
        }

        void F2(TestClass c)
        {
            byte[] arr2 = new byte[] { 0x1, 0x2 };
            c.arr = arr2;
        }

        void F1(byte[] arr)
        {
            byte[] arr2 = new byte[] { 0x1, 0x2 };
            arr = arr2;
        }

        [TestMethod()]
        public void ArrayTest()
        {
            byte[] arr1 = null;

            // Example 1 - array passed as a parameter
            F1(arr1);

            if (arr1 == null)
                Debug.WriteLine("Standalone array is null");
            else
                Debug.WriteLine($"Standalone array size: {arr1.Length}");
            // Example 1 output: "Standalone array is null"

            // Example 2 - array in the class is passed as a parameter
            TestClass c2 = new TestClass();
            F1(c2.arr);
            if (c2.arr == null)
                Debug.WriteLine("\nArray in the class c2 is null");
            else
                Debug.WriteLine($"\nArray size in the class c2: {c2.arr.Length}");
            // Example 2 output: "Array in the class c2 is null"

            // Example 3 - class is passed as a parameter
            TestClass c3 = new TestClass();
            F2(c3);

            if (c3.arr == null)
                Debug.WriteLine("\nArray in the class c3 is null");
            else
                Debug.WriteLine($"\nArray size in the class c3: {c3.arr.Length}");
            // Example 3 output: Array size in the class c3: 2

        }

    }
}

为什么示例3中的输出与示例1和示例2不同？我希望它是相同的，但事实并非如此。

Why is the output in Example 3 is different from Example 1 and Example 2? I would expect it to be the same but it isn't.

推荐答案

要将其作为参考传递，您需要使用ref或out关键字。您将看到您将得到不同的结果。

To pass it as reference you need to do it by using the ref or out keyword. You will see that you'll get a different result.

这是一个简单的测试，可视化您的原始方法不会影响初始字节[]：

Here is a simple test to visualize that your oriiginal method doesn't affect the initial byte[]:

static void F1(byte[] arr, TestClass c)
{
    byte[] arr2 = new byte[] { 0x1, 0x2 };
    arr = arr2;

    if (arr == c.arr)
    {
	Debug.WriteLine("Both variables reference the same object on the heap.");
    }
    else
    {
	Debug.WriteLine("Each variable references its own object.");
    }
}

TestClass c2 = new TestClass();
F1(c2.arr, c2);

如果你现在使用ref关键字

If you now use the ref keyword

static void F1(ref byte[] arr, TestClass c)
{
    byte[] arr2 = new byte[] { 0x1, 0x2 };
    arr = arr2;

    if (arr == c.arr)
    {
	Console.WriteLine("Both variables reference the same object on the heap.");
    }
    else
    {
	Console.WriteLine("Each variable references its own object.");
    }
}

TestClass c2 = new TestClass();
F1(ref c2.arr, c2);

您将看到两个变量都将引用同一个对象。有关详情，请向Jon Skeet推荐
。

you will see that both variables will reference the same object. For more details I recommendthis article by Jon Skeet.

wizend

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