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ii.4.1-hello-world.md

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II.4.1 "Hello world!"

To get the general feel of ILAsm, consider the following simple example, which prints the well known "Hello world!" salutation. The salutation is written by calling WriteLine, a static method found in the class System.Console that is part of the standard assembly mscorlib (see Partition IV).

[Example:

.assembly extern mscorlib {}
.assembly hello {}
.method static public void main() cil managed
{ .entrypoint
  .maxstack 1
  ldstr "Hello world!"
  call void [mscorlib]System.Console::WriteLine(class System.String)
  ret
}

end example]

The .assembly extern declaration references an external assembly, mscorlib, which contains the definition of System.Console. The .assembly declaration in the second line declares the name of the assembly for this program. (Assemblies are the deployment unit for executable content for the CLI.) The .method declaration defines the global method main, the body of which follows, enclosed in braces. The first line in the body indicates that this method is the entry point for the assembly (.entrypoint), and the second line in the body specifies that it requires at most one stack slot (.maxstack).

Method main contains only three instructions: ldstr, call, and ret. The ldstr instruction pushes the string constant "Hello world!" onto the stack and the call instruction invokes System.Console::WriteLine, passing the string as its only argument. (Note that string literals in CIL are instances of the standard class System.String.) As shown, call instructions shall include the full signature of the called method. Finally, the last instruction, ret, returns from main.