初识.Net IL

一.IL基本资料

1.IL概述

　　IL是.NET框架中中间语言（Intermediate Language）的缩写。使用.NET框架提供的编译器可以直接将源程序编译为.exe或.dll文件，但此时编译出来的程序代码并不是CPU能直接执行的机器代码，而是一种中间语言IL（Intermediate Language）的代码(来源百度)

2.查看IL的工具资料

　　查看IL的工具和IL指令详细网上都有很多，我在这推荐几个我认为比较好用的。

1). ILdasm

　　安装VS的时候会安装一款IL查看工具，【ildasm】，位于：C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6 Tools，依据版本不同可能实际路径不一样，但都位于：C:\Program Files (x86)\Microsoft SDKs\Windows目录下

2). ILSpy

　　一款开源的C#反编译工具，个人比较喜欢用这个看，因为对于关键字有颜色标记，IL指令还能直接导航到微软网站查看此指令的解释，下载地址：点这里

3).Reflector

　　当然还有老牌的Reflector，不过要注册。。。

4).IL指令详细

　　这个网上有很多，MSDN上也有说明，我推荐一位博友的帖子 -->>> 点这里

3.IL运行空间

　　　　　　

　　　　　　Managed Heap（托管堆）：这就是NET中的托管堆，用来存放引用类型，它是由GC（垃圾回收器自动进行回收）管理，每个进程共享此空间；

　　　　　　Call Stack（调用堆栈）：每个线程都有自己专属的调用堆栈， 保存运行期间所调用的方法，方法参数，返回地址，以及局部变量,当方法调用完毕后，会丢弃相关信息

　　　　　　Evaluation Stack（计算堆栈）：每个线程都有自己的线程栈，IL 里面的任何计算，都发生在 Evaluation Stack 上，其实就是一个 Stack 结构。可以 Push，也可以 Pop。

二.完整示例代码

C#代码：

  static void Main(string[] args)
         {
             int i = ;
             int j = i + ;
             List<string> list = new List<string>()
             {
                 "","","","",""
             };
             IEnumerator<string> listt = list.GetEnumerator();
             while (listt.MoveNext())
             {
                 Console.WriteLine(listt.Current);
             }

             foreach (var item in list)
             {
                 Console.WriteLine(item);
             }

             Console.ReadLine();
         }
     }

C#代码

IL代码：

.class private auto ansi beforefieldinit SomeThingTest.Program
    extends [mscorlib]System.Object
{
    // 方法
    .method private hidebysig static
        void Main (
            string[] args
        ) cil managed
    {
        // 方法起始 RVA 地址 0x2050
        // 方法起始地址（相对于文件绝对值：0x0250）
        // 代码长度 176 (0xb0)
        .maxstack
        .entrypoint
        .locals init (
            [] int32,
            [] int32,
            [] class [mscorlib]System.Collections.Generic.List`<string>,
            [] class [mscorlib]System.Collections.Generic.IEnumerator`<string>,
            [] bool,
            [] valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<string>,
            [] string
        )

        // 0x025C: 00
        IL_0000: nop
        // 0x025D: 16
        IL_0001: ldc.i4.0
        // 0x025E: 0A
        IL_0002: stloc.0
        // 0x025F: 06
        IL_0003: ldloc.0
        // 0x0260: 1B
        IL_0004: ldc.i4.5
        // 0x0261: 58
        IL_0005: add
        // 0x0262: 0B
        IL_0006: stloc.1
        // 0x0263: 73 0F 00 00 0A
        IL_0007: newobj instance void class [mscorlib]System.Collections.Generic.List`<string>::.ctor()
        // 0x0268: 25
        IL_000c: dup
        // 0x0269: 72 01 00 00 70
        IL_000d: ldstr ""
        // 0x026E: 6F 10 00 00 0A
        IL_0012: callvirt instance void class [mscorlib]System.Collections.Generic.List`<string>::Add(!)
        // 0x0273: 00
        IL_0017: nop
        // 0x0274: 25
        IL_0018: dup
        // 0x0275: 72 05 00 00 70
        IL_0019: ldstr ""
        // 0x027A: 6F 10 00 00 0A
        IL_001e: callvirt instance void class [mscorlib]System.Collections.Generic.List`<string>::Add(!)
        // 0x027F: 00
        IL_0023: nop
        // 0x0280: 25
        IL_0024: dup
        // 0x0281: 72 09 00 00 70
        IL_0025: ldstr ""
        // 0x0286: 6F 10 00 00 0A
        IL_002a: callvirt instance void class [mscorlib]System.Collections.Generic.List`<string>::Add(!)
        // 0x028B: 00
        IL_002f: nop
        // 0x028C: 25
        IL_0030: dup
        // 0x028D: 72 0D 00 00 70
        IL_0031: ldstr ""
        // 0x0292: 6F 10 00 00 0A
        IL_0036: callvirt instance void class [mscorlib]System.Collections.Generic.List`<string>::Add(!)
        // 0x0297: 00
        IL_003b: nop
        // 0x0298: 25
        IL_003c: dup
        // 0x0299: 72 11 00 00 70
        IL_003d: ldstr ""
        // 0x029E: 6F 10 00 00 0A
        IL_0042: callvirt instance void class [mscorlib]System.Collections.Generic.List`<string>::Add(!)
        // 0x02A3: 00
        IL_0047: nop
        // 0x02A4: 0C
        IL_0048: stloc.2
        // 0x02A5: 08
        IL_0049: ldloc.2
        // 0x02A6: 6F 11 00 00 0A
        IL_004a: callvirt instance valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<!> class [mscorlib]System.Collections.Generic.List`<string>::GetEnumerator()
        // 0x02AB: 8C 02 00 00 1B
        IL_004f: box valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<string>
        // 0x02B0: 0D
        IL_0054: stloc.3
        // 0x02B1: 2B 0E
        IL_0055: br.s IL_0065
        // 循环开始 (head: IL_0065)
            // 0x02B3: 00
            IL_0057: nop
            // 0x02B4: 09
            IL_0058: ldloc.3
            // 0x02B5: 6F 12 00 00 0A
            IL_0059: callvirt instance ! class [mscorlib]System.Collections.Generic.IEnumerator`<string>::get_Current()
            // 0x02BA: 28 13 00 00 0A
            IL_005e: call void [mscorlib]System.Console::WriteLine(string)
            // 0x02BF: 00
            IL_0063: nop
            // 0x02C0: 00
            IL_0064: nop

            // 0x02C1: 09
            IL_0065: ldloc.3
            // 0x02C2: 6F 14 00 00 0A
            IL_0066: callvirt instance bool [mscorlib]System.Collections.IEnumerator::MoveNext()
            // 0x02C7: 13 04
            IL_006b: stloc.s
            // 0x02C9: 11 04
            IL_006d: ldloc.s
            // 0x02CB: 2D E6
            IL_006f: brtrue.s IL_0057
        // 循环结束

        // 0x02CD: 00
        IL_0071: nop
        // 0x02CE: 08
        IL_0072: ldloc.2
        // 0x02CF: 6F 11 00 00 0A
        IL_0073: callvirt instance valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<!> class [mscorlib]System.Collections.Generic.List`<string>::GetEnumerator()
        // 0x02D4: 13 05
        IL_0078: stloc.s
        .try
        {
            // 0x02D6: 2B 13
            IL_007a: br.s IL_008f
            // 循环开始 (head: IL_008f)
                // 0x02D8: 12 05
                IL_007c: ldloca.s
                // 0x02DA: 28 15 00 00 0A
                IL_007e: call instance ! valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<string>::get_Current()
                // 0x02DF: 13 06
                IL_0083: stloc.s
                // 0x02E1: 00
                IL_0085: nop
                // 0x02E2: 11 06
                IL_0086: ldloc.s
                // 0x02E4: 28 13 00 00 0A
                IL_0088: call void [mscorlib]System.Console::WriteLine(string)
                // 0x02E9: 00
                IL_008d: nop
                // 0x02EA: 00
                IL_008e: nop

                // 0x02EB: 12 05
                IL_008f: ldloca.s
                // 0x02ED: 28 16 00 00 0A
                IL_0091: call instance bool valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<string>::MoveNext()
                // 0x02F2: 2D E4
                IL_0096: brtrue.s IL_007c
            // 循环结束

            // 0x02F4: DE 0F
            IL_0098: leave.s IL_00a9
        } // .try 结束
        finally
        {
            // 0x02F6: 12 05
            IL_009a: ldloca.s
            // 0x02F8: FE 16 02 00 00 1B
            IL_009c: constrained. valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<string>
            // 0x02FE: 6F 17 00 00 0A
            IL_00a2: callvirt instance void [mscorlib]System.IDisposable::Dispose()
            // 0x0303: 00
            IL_00a7: nop
            // 0x0304: DC
            IL_00a8: endfinally
        } // 捕捉结束

        // 0x0305: 28 18 00 00 0A
        IL_00a9: call string [mscorlib]System.Console::ReadLine()
        // 0x030A: 26
        IL_00ae: pop
        // 0x030B: 2A
        IL_00af: ret
    } // 方法 Program::Main 结束

    .method public hidebysig specialname rtspecialname
        instance void .ctor () cil managed
    {
        // 方法起始 RVA 地址 0x211c
        // 方法起始地址（相对于文件绝对值：0x031c）
        // 代码长度 8 (0x8)
        .maxstack 

        // 0x031D: 02
        IL_0000: ldarg.0
        // 0x031E: 28 19 00 00 0A
        IL_0001: call instance void [mscorlib]System.Object::.ctor()
        // 0x0323: 00
        IL_0006: nop
        // 0x0324: 2A
        IL_0007: ret
    } // 方法 Program::.ctor 结束

} // 类 SomeThingTest.Program 结束

IL代码

　　接下来我会一步一步分析代码，鉴于我也是初学，很多不懂的地方我也不敢乱说，只介绍我了解的，如果不对，谢谢指出。

三.简单分析IL代码

1.IL关键字说明

　　

　　.class:说明这是一个class，这个很简单一看就懂

　　.method:说明这是一个方法，也很简单

　　private，public：访问修饰符，也不多说

　　hidebysig：相当于 new

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" alt="" />

　　.entrypoint:表示程序的入口

　　.locals init:本方法所使用的变量，只是对Call Stack的一个具体展现，这所使用的变量包含程序中正常声明的，以及运行中需要的 ,例： while (listt.MoveNext())，这个循环需要一个bool变量，在编译的时候这个变量是被声明在Call Stack中的，展现于.locals init。

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" alt="" />

　　.maxstack:对于这个我详细讲下，此表示本方法运行时，【同时】需要的最大的栈大小，也就是Evaluation Stack的最大深度。怎么理解这个最大深度？

　　举个栗子：

 int a = ;
 int b = ;
 int c = ;
 int d = a + b + c;
 Console.WriteLine(d);

C#代码

    // 方法
    .method public hidebysig
        instance void test () cil managed
    {
        // 方法起始 RVA 地址 0x2144
        // 方法起始地址（相对于文件绝对值：0x0344）
        // 代码长度 21 (0x15)
        .maxstack
        .locals init (
            [] int32,
            [] int32,
            [] int32,
            [] int32
        )

        // 0x0350: 00
        IL_0000: nop
        // 0x0351: 17
        IL_0001: ldc.i4.
        // 0x0352: 0A
        IL_0002: stloc.
        // 0x0353: 18
        IL_0003: ldc.i4.
        // 0x0354: 0B
        IL_0004: stloc.
        // 0x0355: 19
        IL_0005: ldc.i4.
        // 0x0356: 0C
        IL_0006: stloc.
        // 0x0357: 06
        IL_0007: ldloc.
        // 0x0358: 07
        IL_0008: ldloc.
        // 0x0359: 58
        IL_0009: add
        // 0x035A: 08
        IL_000a: ldloc.
        // 0x035B: 58
        IL_000b: add
        // 0x035C: 0D
        IL_000c: stloc.
        // 0x035D: 09
        IL_000d: ldloc.
        // 0x035E: 28 1A 00 00 0A
        IL_000e: call void [mscorlib]System.Console::WriteLine(int32)
        // 0x0363: 00
        IL_0013: nop
        // 0x0364: 2A
        IL_0014: ret
    } // 方法 testtest::test 结束

IL代码

　　　　IL_0000~IL_0006：此段为声明变量，并加载到Call Stack（调用堆栈）上，过程为：通过指令加载具体的【数值】到Evaluation Stack（计算堆栈），然后弹出并赋值到Call Stack（调用堆栈）

　　　　IL_0007: ldloc.0：加载索引为0的局部到堆栈上，换种说法就是说：从Call Stack加载索引为0的变量到Evaluation Stack中，此时栈的深度为【1】

　　　　IL_0008: ldloc.1：加载索引为1的局部到堆栈上，此时栈的深度为【2】

　　　　IL_0009: add：将两个值相加并将结果推送到计算堆栈上。此步骤我个人是这样理解的：计算完成后会清空加载到栈上的两个值，此时栈的深度为【0】；并将计算出的值放入栈，此时栈的深度为【1】

　　　　所以 a + b + c，是两两相加，直到计算完成，所以最大的栈深度为【2】

　　　　对于.maxstack，有个方法比较特殊，那就是构造方法，【.maxstack 8】，这点其实我不是很明白，我看过很多都是8，不知是默认的，还是怎么的，如果知道的友友，还请留下你的见解

2.逐句分析代码

　　C#对照编译的IL逐句分析，每句IL后面都有该指令详细说明

1).片段1

  int i = ;
  int j = i + ;

C#代码

 // 0x025C: 00
 IL_0000: nop //无操作
 // 0x025D: 16
 IL_0001: ldc.i4.0 //将数值【0】推送到计算堆栈上
 // 0x025E: 0A
 IL_0002: stloc.0 //弹出计算堆栈顶部的值并赋值到调用堆栈索引为0的位置（也就是把刚才推送到的0赋值到调用堆栈索引为0的位置）
 // 0x025F: 06
 IL_0003: ldloc.0 //从调用堆栈上索引为0位置的值加载到计算堆栈上
 // 0x0260: 1B
 IL_0004: ldc.i4.5 //将数值【5】推送到计算堆栈上
 // 0x0261: 58
 IL_0005: add //相加，并将结果推送到计算堆栈上
 // 0x0262: 0B
 IL_0006: stloc.1 //弹出计算堆栈顶部的值并赋值到调用堆栈索引为1的位置（也就是把刚才相加的结果赋值到调用堆栈索引为1的位置）

IL代码

2).片段2

  List<string> list = new List<string>()
  {
      "","","","",""
 };

C#代码

 // 0x0263: 73 0F 00 00 0A
 IL_0007: newobj instance void class [mscorlib]System.Collections.Generic.List`<string>::.ctor() //创建一个类型为List<string>的对象并推送到计算堆栈上，此时栈深度为【1】
 // 0x0268: 25
 IL_000c: dup //复制计算堆栈顶部的值，复制引用，并推送到计算堆栈上，此时深度为【2】
 // 0x0269: 72 01 00 00 70
 IL_000d: ldstr "" //加载字符串【1】到计算堆栈上，此时深度为【3】
 // 0x026E: 6F 10 00 00 0A
 IL_0012: callvirt instance void class [mscorlib]System.Collections.Generic.List`<string>::Add(!) //调用Add方法，完成后清空刚才参与运算的变量，也就是List<string> 对象的副本，与字符串【1】,由于此方法没有返回值，并不会推送任何值到计算堆栈上，此时深度为【1】
 // 0x0273: 00
 IL_0017: nop //此位置到IL_0042都是重复此操作
 // 0x0274: 25
 IL_0018: dup
 // 0x0275: 72 05 00 00 70
 IL_0019: ldstr ""
 // 0x027A: 6F 10 00 00 0A
 IL_001e: callvirt instance void class [mscorlib]System.Collections.Generic.List`<string>::Add(!)
 // 0x027F: 00
 IL_0023: nop
 // 0x0280: 25
 IL_0024: dup
 // 0x0281: 72 09 00 00 70
 IL_0025: ldstr ""
 // 0x0286: 6F 10 00 00 0A
 IL_002a: callvirt instance void class [mscorlib]System.Collections.Generic.List`<string>::Add(!)
 // 0x028B: 00
 IL_002f: nop
 // 0x028C: 25
 IL_0030: dup
 // 0x028D: 72 0D 00 00 70
 IL_0031: ldstr ""
 // 0x0292: 6F 10 00 00 0A
 IL_0036: callvirt instance void class [mscorlib]System.Collections.Generic.List`<string>::Add(!)
 // 0x0297: 00
 IL_003b: nop
 // 0x0298: 25
 IL_003c: dup
 // 0x0299: 72 11 00 00 70
 IL_003d: ldstr ""
 // 0x029E: 6F 10 00 00 0A
 IL_0042: callvirt instance void class [mscorlib]System.Collections.Generic.List`<string>::Add(!)
 // 0x02A3: 00
 IL_0047: nop //无操作
 // 0x02A4: 0C
 IL_0048: stloc.2 //弹出顶部的值并放入调用堆栈索引为【2】的位置，此时深度为【0】

IL代码

3).片段3

 IEnumerator<string> listt = list.GetEnumerator();
 while (listt.MoveNext())
 {
     Console.WriteLine(listt.Current);
 }

C#代码

 IL_0049: ldloc.2 //加载调用堆栈索引为2的值到计算堆栈上，此时深度为【1】
 // 0x02A6: 6F 11 00 00 0A
 IL_004a: callvirt instance valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<!> class [mscorlib]System.Collections.Generic.List`<string>::GetEnumerator() //调用GetEnumerator()，并将返回值推送到计算堆栈上，注意【GetEnumerator()，返回的是Enumerator类型，此类型是个结构，是值类型，明白这一点才清楚下一步】，此时深度为【1】
 // 0x02AB: 8C 02 00 00 1B
 IL_004f: box valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<string> //进行装箱，转换成object类型，因为上一步返回的是值类型，所以在这一步进行装箱，过程：弹出上一步返回的值，进行装箱，并将对象的引用推送到计算堆栈上，此时深度为【1】
 // 0x02B0: 0D
 IL_0054: stloc.3 //弹出顶部的值，并放入调用堆栈索引为3的位置 此时深度为【0】
 // 0x02B1: 2B 0E
 IL_0055: br.s IL_0065 // 直接跳转到 IL_0065处，开始循环
 // 循环开始 (head: IL_0065)
 // 0x02B3: 00
 IL_0057: nop //无操作
 // 0x02B4: 09
 IL_0058: ldloc.3 //加载调用堆栈中索引为3的值推送到计算堆栈，此时深度为【1】
 // 0x02B5: 6F 12 00 00 0A
 IL_0059: callvirt instance ! class [mscorlib]System.Collections.Generic.IEnumerator`<string>::get_Current() //调用get_Current()，将返回值推送到计算堆栈上，此时深度为【1】
 // 0x02BA: 28 13 00 00 0A
 IL_005e: call void [mscorlib]System.Console::WriteLine(string) //调用WriteLine方法，此时深度为【0】
 // 0x02BF: 00
 IL_0063: nop //无操作
 // 0x02C0: 00
 IL_0064: nop //无操作

 // 0x02C1: 09
 IL_0065: ldloc.3 //加载调用堆栈中索引为3的值推送到计算堆栈，此时深度为【1】
 // 0x02C2: 6F 14 00 00 0A
 IL_0066: callvirt instance bool [mscorlib]System.Collections.IEnumerator::MoveNext() //调用MoveNext()，返回的bool  推送到计算堆栈上 ，此时深度为【1】
 // 0x02C7: 13 04
 IL_006b: stloc.s  // 弹出顶的值，放入调用堆栈索引为4的位置，此时深度为【0】
 // 0x02C9: 11 04
 IL_006d: ldloc.s  //加载调用堆栈中索引为4的值推送到计算堆栈，此时深度为【1】
 // 0x02CB: 2D E6
 IL_006f: brtrue.s IL_0057 //如果为 true、非空或非零，则跳转到IL_0057的位置，此时深度为【0】
 // 循环结束

IL代码

4).片段4

 foreach (var item in list)
 {
     Console.WriteLine(item);
  }

 Console.ReadLine();

C#代码

 // 0x02CD: 00
 IL_0071: nop //无操作
 // 0x02CE: 08
 IL_0072: ldloc.2 //加载调用堆栈中索引为2的值推送到计算堆栈，此时深度为【1】
 // 0x02CF: 6F 11 00 00 0A
 IL_0073: callvirt instance valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<!> class [mscorlib]System.Collections.Generic.List`<string>::GetEnumerator()//调用GetEnumerator() ，因为foreach的对象本身就是一个可迭代的对象，所以是使用迭代器，返回值同样是一个值类型，但是没有变量接收，所以不需要装箱，此时深度为【1】
 // 0x02D4: 13 05
 IL_0078: stloc.s  //弹出顶部的值，放入调用堆栈索引为5的位置，此时深度为【0】
 .try
 {
     // 0x02D6: 2B 13
     IL_007a: br.s IL_008f //跳转到IL_008f
     // 循环开始 (head: IL_008f)
     // 0x02D8: 12 05
     IL_007c: ldloca.s  //加载调用堆栈中索引为5的值推送到计算堆栈，此时深度为【1】
     // 0x02DA: 28 15 00 00 0A
     IL_007e: call instance ! valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<string>::get_Current() //调用get_Current() 获取当前迭代器当前位置的值 ，此时深度为【1】
     // 0x02DF: 13 06
     IL_0083: stloc.s  // 弹出顶的值，放入调用堆栈索引为6的位置，此时深度为【0】
     // 0x02E1: 00
     IL_0085: nop //无操作
     // 0x02E2: 11 06
     IL_0086: ldloc.s  //加载调用堆栈中索引为6的值推送到计算堆栈，此时深度为【1】
     // 0x02E4: 28 13 00 00 0A
     IL_0088: call void [mscorlib]System.Console::WriteLine(string) //调用WriteLine方法，此时深度为【0】
     // 0x02E9: 00
     IL_008d: nop //无操作
     // 0x02EA: 00
     IL_008e: nop //无操作

     // 0x02EB: 12 05
     IL_008f: ldloca.s  //加载调用堆栈中索引为5的值推送到计算堆栈，此时深度为【1】
     // 0x02ED: 28 16 00 00 0A
     IL_0091: call instance bool valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<string>::MoveNext() //调用MoveNext() 返回值为bool ，此时深度为【1】
     // 0x02F2: 2D E4
     IL_0096: brtrue.s IL_007c //如果为 true、非空或非零，则跳转到IL_007c的位置，此时深度为【0】
     // 循环结束

     // 0x02F4: DE 0F
     IL_0098: leave.s IL_00a9 //退出受保护的代码区域，跳转到IL_00a9
 } // .try 结束
 finally
 {
     // 0x02F6: 12 05
     IL_009a: ldloca.s  //加载调用堆栈中索引为5的值推送到计算堆栈，此时深度为【1】 ，说明下：这个值是循环是的迭代器对象
     // 0x02F8: FE 16 02 00 00 1B
     IL_009c: constrained. valuetype [mscorlib]System.Collections.Generic.List`/Enumerator<string> //约束要对其进行虚方法调用的类型。 这里的话，清楚Call与Callvirt区别就知道为啥要这样了。。。我不是很了解这个，不敢乱说，望知道的友友留下你的见解，关于【constrained】指令的解释： https://msdn.microsoft.com/library/system.reflection.emit.opcodes.constrained.aspx
     // 0x02FE: 6F 17 00 00 0A
     IL_00a2: callvirt instance void [mscorlib]System.IDisposable::Dispose() //调用Dispose()，释放迭代器，此时深度为【0】
     // 0x0303: 00
     IL_00a7: nop //无操作
     // 0x0304: DC
     IL_00a8: endfinally //结束捕获
 } // 捕捉结束
 // 0x0305: 28 18 00 00 0A
 IL_00a9: call string [mscorlib]System.Console::ReadLine() //调用ReadLine()，此时深度为【1】
 // 0x030A: 26
 IL_00ae: pop //移除当前位于计算堆栈顶部的值。 对于这个我是这样理解的：ReadLine() 会返回要给string类型的值，但是没有变量接收，所以会移除这个值
 // 0x030B: 2A
 IL_00af: ret //从当前方法返回，并将返回值（如果存在）从调用方的计算堆栈推送到被调用方的计算堆栈上。

IL代码

四.结尾

　　以上都是本人的个人理解，如果不对，谢谢指出！

　　分享个我当时遇到过的题目：

List<string> _List = new List<string>();
public string this[int i]
{
    get { return _List[i]; }
}

public string get_Item(int i)
{
    return _List[i];
}

C#代码

　　问：这段代码有错么，如果有错在哪呢？