The Assembly Manifest in Visual C#

Creator DataMatrix in Visual C# The Assembly Manifest

The term manifest comes from the Latin manifestus, which means blatant, obvious. It was later used in the shipping industry to mean the list of cargo and passengers on a ship or train. To find a particular passenger or to discover what cargo is contained on a train, you would consult the manifest. The assembly manifest serves the same purpose for an assembly. The runtime uses the manifest to find information about what types are in an assembly, and where to find those types in the assembly. Because of the information in the manifest, the assembly is said to be self-describing. This presents a significant advance from unmanaged executables and DLLs, which do not have such rich data describing themselves. This rich metadata makes it easier to dynamically load assemblies and start executing the code in them.

You can familiarize yourself with the basics of assemblies and metadata by compiling a simple C++/CLI program and looking at the resulting output using a tool called ILDasm.exe. ILDasm means Intermediate Language Disassembler. Consider the simple C++ program in Listing 3-1. Listing 3-1. A Simple C++/CLI Program // reftype.cpp using namespace System; ref class RefType { String^ classname; public: RefType() { classname = gcnew String("RefType"); } String^ GetMessage() { return String::Format("I am a " + classname); } }; int main() { RefType^ r = gcnew RefType(); Console::WriteLine(r->GetMessage()); } You must compile it (in Visual C++) with the /clr option. Any of the variants of the /clr option are acceptable, but the ILDasm.exe display is simpler if you use the /clr:safe option, since that option avoids bringing in a lot of plumbing used to support native code constructs. cl.exe /clr:safe reftype.cpp This produces the executable reftype.exe. As in classic C++, you also have the option of producing an object file first, and then later linking to produce an executable. None of these basics have changed. In fact, the file name doesn t look any different. What has changed is that the resulting executable is an assembly with managed code, not a native executable. When it is executed, it will actually fire up the CLR and run in a managed context.

You can view the metadata for reftype.exe by running ILDasm.exe. You can find ILDasm.exe in your .NET Framework SDK Bin directory. You may want to add this directory to the PATH environment variable so you always have access to ILDasm, since it is so useful. For example, it might be C:\Program Files\Microsoft Visual Studio 8\SDK\2.0\Bin or C:\Program Files\ Microsoft SDKs\Windows\v6.0A\bin. Figure 3-1 shows ILDasm.exe displaying information about reftype.exe.

Figure 3-1. ILDasm.exe in GUI mode Use the /text option if you just want text output to the console, instead of a GUI. Here s the output of the command line Ildasm.exe reftype.exe /text: // Microsoft (R) .NET Framework IL Disassembler. Version 2.0.50727.42 // Copyright (c) Microsoft Corporation. All rights reserved.

// Metadata version: v2.0.50727 .assembly extern mscorlib { .publickeytoken = (B7 7A 5C 56 19 34 E0 89 ) .hash = (8B 15 F4 76 87 23 8A E0 94 A8 8B 19 BF 0F 87 C9 F0 97 3C C3 ) .ver 2:0:0:0 } .assembly reftype { .hash algorithm 0x00008004 .ver 0:0:0:0 }

.module reftype.exe // MVID: {8C21FB19-23D0-45E2-87BD-20EC172CF3CA} .imagebase 0x00400000 .file alignment 0x00000200 .stackreserve 0x00100000 .subsystem 0x0003 // WINDOWS_CUI .corflags 0x00000001 // ILONLY // Image base: 0x02EC0000

// ================== GLOBAL METHODS ========================= .method assembly static int32 main() cil managed { .entrypoint // Code size 19 (0x13) .maxstack 1 .locals init (class RefType V_0) IL_0000: newobj instance void RefType::.ctor() IL_0005: stloc.0 IL_0006: ldloc.0 IL_0007: call instance string RefType::GetMessage() IL_000c: call void [mscorlib]System.Console::WriteLine(string) IL_0011: ldc.i4.0 IL_0012: ret } // end of global method main

// =============================================================

// =============== CLASS MEMBERS DECLARATION =================== .class private auto ansi beforefieldinit RefType extends [mscorlib]System.Object { .field private string classname .method public hidebysig specialname rtspecialname instance void .ctor() cil managed { // Code size 18 (0x12) .maxstack 2 IL_0000: ldarg.0 IL_0001: call instance void [mscorlib]System.Object::.ctor() IL_0006: ldarg.0 IL_0007: ldstr "MyRefType"