params、ref及out(C#)
1:Params
using System;
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class App
{
public static void UseRef(ref int i)
{
i += 100;
Console.WriteLine("i = {0}", i);
}
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static void Main()
{
int i = 10;
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// 查看调用方法之前的值
Console.WriteLine("Before the method calling: i = {0}", i);
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UseRef(ref i);
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// 查看调用方法之后的值
Console.WriteLine("After the method calling: i = {0}", i);
Console.Read();
}
}
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/**//*
控制台输出:
Before the method calling : i = 10
i = 110
After the method calling: i = 110
*/
这与 ref 关键字类似。与 ref 的不同之处:
1:ref 要求变量必须在传递之前进行初始化。
2:尽管作为 out 参数传递的变量不需要在传递之前进行初始化,但需要调用方法以便在方法返回之前赋值。
示例:与 ref 示例不同的地方只要将 ref 改为 out,然后变量 i 仅需要声明即可。
static void Main()
{
//int i = 10; 改为
int i;
//
}
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public static void UseParams(params object[] list)
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{
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for (int i = 0; i < list.Length; i++)
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{
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Console.WriteLine(list[i]);
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}
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}
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static void Main()
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{
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// 一般做法是先构造一个对象数组,然后将此数组作为方法的参数
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object[] arr = new object[3] { 100, 'a', "keywords" };
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UseParams(arr);
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// 而使用了params修饰方法参数后,我们可以直接使用一组对象作为参数
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// 当然这组参数需要符合调用的方法对参数的要求
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UseParams(100, 'a', "keywords");
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Console.Read();
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}
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注意: 在方法声明中的 params 关键字之后不允许任何其他参数,并且在方法声明中只允许一个 params 关键字。
2:Ref与Out
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注意:
1:若要使用 ref 参数,则方法定义和调用方法都必须显式使用 ref 关键字。
2:传递到 ref 参数的参数必须最先初始化。这与 out 不同,out 的参数在传递之前不需要显式初始化。
3:属性不是变量,因此不能作为 ref 参数传递。
4:尽管 ref 和 out 在运行时的处理方式不同,但它们在编译时的处理方式是相同的。因此,如果一个方法采用 ref 参数,而另一个方法采用 out 参数,则无法重载这两个方法。例如,从编译的角度来看,以下代码中的两个方法是完全相同的。如果尝试这么做,将导致不能编译该代码。
5:如果一个方法采用 ref 或 out 参数,而另一个方法不采用这两类参数,则可以进行重载。
6:Ref后可以为引用类型
这与 ref 关键字类似。与 ref 的不同之处:
1:ref 要求变量必须在传递之前进行初始化。
2:尽管作为 out 参数传递的变量不需要在传递之前进行初始化,但需要调用方法以便在方法返回之前赋值。
示例:与 ref 示例不同的地方只要将 ref 改为 out,然后变量 i 仅需要声明即可。
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