C#中的 ref 和 out
使用C#一年多了,竟然是昨天才知道C# 中有 ref 和 out的用法
于是看了一会儿demo,大致搞懂是啥东西了。
这种方法的优点就是可以返回多个值,不再受函数返回一个值的限制,很爽。
其实也很简单,就好像C++里的&(引用)
传递的是实际参数的地址,修改参数值,就会导致直接将内存中该地址中的值修改掉
所以之后输出该参数的值将是修改之后的值
需要注意的是:属性不是变量,不能作为 out 参数传递。
还有如下重载也是不允许的
对于ref 和 out给个简单的demo
相信一看就明白了
输出
The value before calling the method: 5
The value inside the method: 25
The value after calling the method: 25
代码讨论
本示例中,传递的不是 myInt 的值,而是对 myInt 的引用。参数 x 不是 int 类型,它是对 int 的引用(本例中为对 myInt 的引用)。因此,当在方法内对 x 求平方时,实际被求平方的是 x 所引用的项:myInt。
但是ref 和 out 也存在一些区别:
于是看了一会儿demo,大致搞懂是啥东西了。
这种方法的优点就是可以返回多个值,不再受函数返回一个值的限制,很爽。
其实也很简单,就好像C++里的&(引用)
传递的是实际参数的地址,修改参数值,就会导致直接将内存中该地址中的值修改掉
所以之后输出该参数的值将是修改之后的值
需要注意的是:属性不是变量,不能作为 out 参数传递。
还有如下重载也是不允许的
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class MyClass
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{
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public void MyMethod(out int i) {i = 10;}
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public void MyMethod(ref int i) {i = 10;}
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}
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对于ref 和 out给个简单的demo
相信一看就明白了
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// PassingParams2.cs
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using System;
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class PassingValByRef
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{
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static void SquareIt(ref int x)
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// The parameter x is passed by reference.
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// Changes to x will affect the original value of myInt.
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{
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x *= x;
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Console.WriteLine("The value inside the method: {0}", x);
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}
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public static void Main()
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{
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int myInt = 5;
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Console.WriteLine("The value before calling the method: {0}",
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myInt);
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SquareIt(ref myInt); // Passing myInt by reference.
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Console.WriteLine("The value after calling the method: {0}",
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myInt);
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}
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}
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输出
The value before calling the method: 5
The value inside the method: 25
The value after calling the method: 25
代码讨论
本示例中,传递的不是 myInt 的值,而是对 myInt 的引用。参数 x 不是 int 类型,它是对 int 的引用(本例中为对 myInt 的引用)。因此,当在方法内对 x 求平方时,实际被求平方的是 x 所引用的项:myInt。
但是ref 和 out 也存在一些区别:
与所有的 out 参数一样,在使用数组类型的 out 参数前必须先为其赋值,即必须由接受方为其赋值。例如:
public static void MyMethod(out int[] arr) { arr = new int[10]; // definite assignment of arr }
与所有的 ref 参数一样,数组类型的 ref 参数必须由调用方明确赋值。因此不需要由接受方明确赋值。可以将数组类型的 ref 参数更改为调用的结果。例如,可以为数组赋以 null 值,或将其初始化为另一个数组。例如:
public static void MyMethod(ref int[] arr) { arr = new int[10]; // arr initialized to a different array }
下面给出两个demo
示例 1
在此例中,在调用方(Main
方法)中声明数组 myArray
,并在 FillArray
方法中初始化此数组。然后将数组元素返回调用方并显示。
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using System;
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class TestOut
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{
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static public void FillArray(out int[] myArray)
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{
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// Initialize the array:
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myArray = new int[5] {1, 2, 3, 4, 5};
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}
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static public void Main()
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{
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int[] myArray; // Initialization is not required
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// Pass the array to the callee using out:
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FillArray(out myArray);
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// Display the array elements:
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Console.WriteLine("Array elements are:");
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for (int i=0; i < myArray.Length; i++)
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Console.WriteLine(myArray[i]);
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}
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}
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输出
Array elements are:
1
2
3
4
5
示例 2
在此例中,在调用方(Main 方法)中初始化数组 myArray,并通过使用 ref 参数将其传递给 FillArray 方法。在 FillArray 方法中更新某些数组元素。然后将数组元素返回调用方并显示。
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using System;
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class TestRef
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{
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public static void FillArray(ref int[] arr)
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{
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// Create the array on demand:
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if (arr == null)
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arr = new int[10];
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// Otherwise fill the array:
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arr[0] = 123;
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arr[4] = 1024;
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}
13![](/Images/OutliningIndicators/InBlock.gif)
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static public void Main ()
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{
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// Initialize the array:
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int[] myArray = {1,2,3,4,5};
18![](/Images/OutliningIndicators/InBlock.gif)
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// Pass the array using ref:
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FillArray(ref myArray);
21![](/Images/OutliningIndicators/InBlock.gif)
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// Display the updated array:
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Console.WriteLine("Array elements are:");
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for (int i = 0; i < myArray.Length; i++)
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Console.WriteLine(myArray[i]);
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}
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}
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输出
Array elements are: 123 2 3 4 1024