CSharp知识点整理记录

 

//////////////////////////////////////////////一些关于Static的记录////////////////////////////////////////////////

注意：当类第一次被加载时，会对类中的静态变量先按顺序进行分配内存空间，当全部分配完内存空间之后，在对静态变量按顺序赋值。
首先分为两部分 寄存器和内存（包括缓存）
内存分为两部分 代码和数据
数据分为两部分 静态存储区和运行时存储
运行时存储分为 堆栈 和 堆
静态存储分为 全局静态存储 和 常量

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

////////////////////////Enum.GetUnderlyingType(Type) Method////////////

using System;

public class Example

{

   public static void Main()

   {

      Enum[] enumValues = { ConsoleColor.Red, DayOfWeek.Monday,

                            MidpointRounding.ToEven, PlatformID.Win32NT,

                            DateTimeKind.Utc, StringComparison.Ordinal };

      Console.WriteLine("{0,-10} {1, 18}   {2,15}\n",

                        "Member", "Enumeration", "Underlying Type");

      foreach (var enumValue in enumValues)

         DisplayEnumInfo(enumValue);

   }

   static void DisplayEnumInfo(Enum enumValue)

   {

      Type enumType = enumValue.GetType();

      Type underlyingType = Enum.GetUnderlyingType(enumType);

      Console.WriteLine("{0,-10} {1, 18}   {2,15}",

                        enumValue, enumType.Name, underlyingType.Name);  

   }

}

// The example displays the following output:

//       Member            Enumeration   Underlying Type

//      

//       Red              ConsoleColor             Int32

//       Monday              DayOfWeek             Int32

//       ToEven       MidpointRounding             Int32

//       Win32NT            PlatformID             Int32

//       Utc              DateTimeKind             Int32

//       Ordinal      StringComparison             Int32

enum Foo : long { One, Two };

And then GetUnderlyingType is going to return long for typeof(Foo).

Note that the underlying type can be any integral type except for char types.

获得大小：Marshal.SizeOf(Enum.GetUnderlyingType(enumType))

///////////////////////////////// HashSet vs. List //////////////////////////////////////////

A lot of people are saying that once you get to the size where speed is actually a concern that HashSet will always beat List, but that depends on what you are doing.

Let's say you have a List that will only ever have on average 5 items in it. Over a large number of cycles, if a single item is added or removed each cycle, you may well be better off using a List.

I did a test for this on my machine, and, well, it has to be very very small to get an advantage from List. For a list of short strings, the advantage went away after size 5, for objects after size 20.

1 item LIST strs time: 617ms

1 item HASHSET strs time: 1332ms

 

2 item LIST strs time: 781ms

2 item HASHSET strs time: 1354ms

 

3 item LIST strs time: 950ms

3 item HASHSET strs time: 1405ms

 

4 item LIST strs time: 1126ms

4 item HASHSET strs time: 1441ms

 

5 item LIST strs time: 1370ms

5 item HASHSET strs time: 1452ms

 

6 item LIST strs time: 1481ms

6 item HASHSET strs time: 1418ms

 

7 item LIST strs time: 1581ms

7 item HASHSET strs time: 1464ms

 

8 item LIST strs time: 1726ms

8 item HASHSET strs time: 1398ms

 

9 item LIST strs time: 1901ms

9 item HASHSET strs time: 1433ms

 

1 item LIST objs time: 614ms

1 item HASHSET objs time: 1993ms

 

4 item LIST objs time: 837ms

4 item HASHSET objs time: 1914ms

 

7 item LIST objs time: 1070ms

7 item HASHSET objs time: 1900ms

 

10 item LIST objs time: 1267ms

10 item HASHSET objs time: 1904ms

 

13 item LIST objs time: 1494ms

13 item HASHSET objs time: 1893ms

 

16 item LIST objs time: 1695ms

16 item HASHSET objs time: 1879ms

 

19 item LIST objs time: 1902ms

19 item HASHSET objs time: 1950ms

 

22 item LIST objs time: 2136ms

22 item HASHSET objs time: 1893ms

 

25 item LIST objs time: 2357ms

25 item HASHSET objs time: 1826ms

 

28 item LIST objs time: 2555ms

28 item HASHSET objs time: 1865ms

 

31 item LIST objs time: 2755ms

31 item HASHSET objs time: 1963ms

 

34 item LIST objs time: 3025ms

34 item HASHSET objs time: 1874ms

 

37 item LIST objs time: 3195ms

37 item HASHSET objs time: 1958ms

 

40 item LIST objs time: 3401ms

40 item HASHSET objs time: 1855ms

 

43 item LIST objs time: 3618ms

43 item HASHSET objs time: 1869ms

 

46 item LIST objs time: 3883ms

46 item HASHSET objs time: 2046ms

 

49 item LIST objs time: 4218ms

49 item HASHSET objs time: 1873ms

Here is that data displayed as a graph:

Here's the code:

static void Main(string[] args)

{

    int times = 10000000;

    for (int listSize = 1; listSize < 10; listSize++)

    {

        List list = new List();

        HashSet hashset = new HashSet();

        for (int i = 0; i < listSize; i++)

        {

            list.Add("string" + i.ToString());

            hashset.Add("string" + i.ToString());

        }

        Stopwatch timer = new Stopwatch();

        timer.Start();

        for (int i = 0; i < times; i++)

        {

            list.Remove("string0");

            list.Add("string0");

        }

        timer.Stop();

        Console.WriteLine(listSize.ToString() + " item LIST strs time: " + timer.ElapsedMilliseconds.ToString() + "ms");

 

        timer = new Stopwatch();

        timer.Start();

        for (int i = 0; i < times; i++)

        {

            hashset.Remove("string0");

            hashset.Add("string0");

        }

        timer.Stop();

        Console.WriteLine(listSize.ToString() + " item HASHSET strs time: " + timer.ElapsedMilliseconds.ToString() + "ms");

        Console.WriteLine();

    }

 

    for (int listSize = 1; listSize < 50; listSize+=3)

    {

        List