定义局部变量const与类const

Question

如果我使用的是仅在方法中需要的常量，那么最好在方法范围内或类范围内声明const？在该方法中是否有更好的性能声明？如果是这样，我认为在类范围（文件顶部）定义它们以更改值并更容易重新编译是更标准的方法。

public class Bob
{
   private const int SomeConst = 100; // declare it here?
   public void MyMethod()
   {
      const int SomeConst = 100; // or declare it here?
      // Do something with SomeConst
   }
}

Answer 1

换句话说，常量不是引用的存储位置。它不像变量，更像文字。常量是在代码中多个位置同步的文字。因此，这取决于您-尽管更精巧的编程是将常量的范围限制在相关的范围内。

Answer 2

Answer 3

代码：

using System;
using System.Diagnostics;

namespace TestVariableScopePerformance
{
    class Program
    {
        static void Main(string[] args)
        {
            TestClass tc = new TestClass();
            Stopwatch sw = new Stopwatch();

            sw.Start();
            tc.MethodGlobal();
            sw.Stop();

            Console.WriteLine("Elapsed for MethodGlobal = {0} Minutes {1} Seconds {2} MilliSeconds", sw.Elapsed.Minutes, sw.Elapsed.Seconds, sw.Elapsed.Milliseconds);
            sw.Reset();

            sw.Start();
            tc.MethodLocal();
            sw.Stop();

            Console.WriteLine("Elapsed for MethodLocal = {0} Minutes {1} Seconds {2} MilliSeconds", sw.Elapsed.Minutes, sw.Elapsed.Seconds, sw.Elapsed.Milliseconds);

            Console.WriteLine("Press any key to continue...");
            Console.ReadKey();
        }


    }

    class TestClass
    {
        const int Const1 = 100;

        internal void MethodGlobal()
        {
            double temp = 0d;
            for (int i = 0; i < int.MaxValue; i++)
            {
                temp = (i * Const1);
            }
        }

        internal void MethodLocal()
        {
            const int Const2 = 100;
            double temp = 0d;
            for (int i = 0; i < int.MaxValue; i++)
            {
                temp = (i * Const2);
            }
        }
    }
}

3次迭代的结果：

Elapsed for MethodGlobal = 0 Minutes 1 Seconds 285 MilliSeconds
Elapsed for MethodLocal = 0 Minutes 1 Seconds 1 MilliSeconds
Press any key to continue...

Elapsed for MethodGlobal = 0 Minutes 1 Seconds 39 MilliSeconds
Elapsed for MethodLocal = 0 Minutes 1 Seconds 274 MilliSeconds
Press any key to continue...

Elapsed for MethodGlobal = 0 Minutes 1 Seconds 305 MilliSeconds
Elapsed for MethodLocal = 0 Minutes 1 Seconds 31 MilliSeconds
Press any key to continue...

我想观察结果会得出@ jnm2答案。

请从您的系统中运行相同的代码，并让我们知道结果。

Answer 4

Answer 5

Answer 6