生成、打包、部署和管理应用程序及类型（2）：元数据概述

托管文件PE（Program.exe）文件由四部分构成：PE32（+）头、CLR头、元数据以及IL。PE32（+）头是Windows要求的标准信息。CLR头是一个小的信息快，是需要CLR的模块特有的。这个头包含模块生成时所面向的CLR的major和minor版本号。最后，CLR头还包含模块内部的一些元数据表的大小和偏移量。

元数据是由3个表构成的二进制数据块:定义表、引用表和清单表。

可以用多种工具检查托管在PE文件中的元数据。例如ILDasm.exe。使用工具，可以看到元数据信息：

===========================================================
ScopeName : Program.exe
MVID      : {8DF25279-3C44-4141-AAFA-6056CDD958E7}
===========================================================
Global functions
-------------------------------------------------------

Global fields
-------------------------------------------------------

Global MemberRefs
-------------------------------------------------------

TypeDef #1 (02000002)
-------------------------------------------------------
    TypDefName: Project_1.Program  (02000002)
    Flags     : [NotPublic] [AutoLayout] [Class] [AnsiClass] [BeforeFieldInit]  (00100000)
    Extends   : 01000001 [TypeRef] System.Object
    Method #1 (06000001) [ENTRYPOINT]
    -------------------------------------------------------
        MethodName: Main (06000001)
        Flags     : [Private] [Static] [HideBySig] [ReuseSlot]  (00000091)
        RVA       : 0x00002050
        ImplFlags : [IL] [Managed]  (00000000)
        CallCnvntn: [DEFAULT]
        ReturnType: Void
        1 Arguments
            Argument #1:  SZArray String
        1 Parameters
            (1) ParamToken : (08000001) Name : args flags: [none] (00000000)

    Method #2 (06000002) 
    -------------------------------------------------------
        MethodName: .ctor (06000002)
        Flags     : [Public] [HideBySig] [ReuseSlot] [SpecialName] [RTSpecialName] [.ctor]  (00001886)
        RVA       : 0x0000205e
        ImplFlags : [IL] [Managed]  (00000000)
        CallCnvntn: [DEFAULT]
        hasThis 
        ReturnType: Void
        No arguments.


TypeRef #1 (01000001)
-------------------------------------------------------
Token:             0x01000001
ResolutionScope:   0x23000001
TypeRefName:       System.Object
    MemberRef #1 (0a000004)
    -------------------------------------------------------
        Member: (0a000004) .ctor: 
        CallCnvntn: [DEFAULT]
        hasThis 
        ReturnType: Void
        No arguments.

TypeRef #2 (01000002)
-------------------------------------------------------
Token:             0x01000002
ResolutionScope:   0x23000001
TypeRefName:       System.Runtime.CompilerServices.CompilationRelaxationsAttribute
    MemberRef #1 (0a000001)
    -------------------------------------------------------
        Member: (0a000001) .ctor: 
        CallCnvntn: [DEFAULT]
        hasThis 
        ReturnType: Void
        1 Arguments
            Argument #1:  I4

TypeRef #3 (01000003)
-------------------------------------------------------
Token:             0x01000003
ResolutionScope:   0x23000001
TypeRefName:       System.Runtime.CompilerServices.RuntimeCompatibilityAttribute
    MemberRef #1 (0a000002)
    -------------------------------------------------------
        Member: (0a000002) .ctor: 
        CallCnvntn: [DEFAULT]
        hasThis 
        ReturnType: Void
        No arguments.

TypeRef #4 (01000004)
-------------------------------------------------------
Token:             0x01000004
ResolutionScope:   0x23000001
TypeRefName:       System.Console
    MemberRef #1 (0a000003)
    -------------------------------------------------------
        Member: (0a000003) WriteLine: 
        CallCnvntn: [DEFAULT]
        ReturnType: Void
        1 Arguments
            Argument #1:  String

Assembly
-------------------------------------------------------
    Token: 0x20000001
    Name : Program
    Public Key    :
    Hash Algorithm : 0x00008004
    Version: 0.0.0.0
    Major Version: 0x00000000
    Minor Version: 0x00000000
    Build Number: 0x00000000
    Revision Number: 0x00000000
    Locale: <null>
    Flags : [none] (00000000)
    CustomAttribute #1 (0c000001)
    -------------------------------------------------------
        CustomAttribute Type: 0a000001
        CustomAttributeName: System.Runtime.CompilerServices.CompilationRelaxationsAttribute :: instance void .ctor(int32)
        Length: 8
        Value : 01 00 08 00 00 00 00 00                          >                <
        ctor args: (8)

    CustomAttribute #2 (0c000002)
    -------------------------------------------------------
        CustomAttribute Type: 0a000002
        CustomAttributeName: System.Runtime.CompilerServices.RuntimeCompatibilityAttribute :: instance void .ctor()
        Length: 30
        Value : 01 00 01 00 54 02 16 57  72 61 70 4e 6f 6e 45 78 >    T  WrapNonEx<
                      : 63 65 70 74 69 6f 6e 54  68 72 6f 77 73 01       >ceptionThrows   <
        ctor args: ()


AssemblyRef #1 (23000001)
-------------------------------------------------------
    Token: 0x23000001
    Public Key or Token: b7 7a 5c 56 19 34 e0 89 
    Name: mscorlib
    Version: 4.0.0.0
    Major Version: 0x00000004
    Minor Version: 0x00000000
    Build Number: 0x00000000
    Revision Number: 0x00000000
    Locale: <null>
    HashValue Blob:
    Flags: [none] (00000000)


User Strings
-------------------------------------------------------
70000001 : ( 4) L"HaHa"


Coff symbol name overhead:  0
===========================================================
===========================================================
===========================================================

无需完全理解这些信息。Program.exe包含名为Project_1.Program（Project_1是工程名字）的TypeDef。Program是公共密封类，从System.Object派生。Program类型还定义了两个方法：Main和.ctor。

Main是公共静态方法，用IL代码实现。Main返回类型是void 。构造器是公共方法，用IL代码实现，返回类型是void，有一个this指针指向调用方法时构造对象的内存。