C# 中静态、只读和常量之间的区别

本文关键字：常量 之间 区别 只读 静态 | 更新日期: 2023-09-19 21:44:09

下表列出了 C# 中 Static 、只读和常量之间的区别。

staticreadonlyconst
使用 static 关键字声明。Declared using the readonly keyword.Declred using the const keyword. By default a const is static that cannot be changed.
类、构造函数、方法、变量、属性、事件和运算符可以是静态的。 结构、索引器、枚举、析构函数或终结器不能是静态的。Only the class level fields can be readonly. The local variables of methods cannot be readonly.Only the class level fields or variables can be constant.
只能在静态方法中访问静态成员。非静态方法无法访问静态成员。Readonly fields can be initialized at declaration or in the constructor.

Therefore, readonly variables are used for the run-time constants.		The constant fields must be initialized at the time of declaration.

Therefore, const variables are used for compile-time constants.
可以使用 ClassName.StaticMemberName 修改静态成员的值。Readonly variable cannot be modified at run-time. It can only be initialized or changed in the constructor.Constant variables cannot be modified after declaration.
静态成员可以使用 ClassName.StaticMemberName 访问，但不能使用 object 访问。Readonly members can be accessed using object, but not ClassName.ReadOnlyVariableName.Const members can be accessed using ClassName.ConstVariableName, but cannot be accessed using object.

下面的示例演示静态、只读和常量变量之间的区别。

示例： static vs readonly vs const

public class Program
{
	public static void Main()
	{
		MyClass mc = new MyClass(50);
		mc.ChangeVal(45);
		mc.Display();
		
		Console.WriteLine("MyClass.constvar = {0}", MyClass.constvar);
		Console.WriteLine("MyClass.staticvar = {0}", MyClass.staticvar);
	}
}
public class MyClass
{
	public readonly int readonlyvar1 = 10, readonlyvar2;
	public const int constvar = 20;
	public static int staticvar = 0;
	public MyClass(int i)
	{
		readonlyvar2 = i; // valid
		//z = i; //compile-time error
		staticvar = i; // valid
	}
	public void ChangeVal(int val)
	{
		//x = val;
		//z = i; //compile-time error
		staticvar = val; // valid
	}
	public void Display()
	{
		Console.WriteLine(staticvar);
		Console.WriteLine(readonlyvar1);
		Console.WriteLine(constvar);
	}
}

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