Reflection.Emit.DeclareLocal and Reflection.Emit.DefineLabel

Working with Reflection.Emit today I ran into two thing that I couldn’t

quickly find answers to. First, was regarding the br.s (OpCodes.Br_S)

code. Secondly, was regarding an error ‘Common Language Runtime

detected an invalid program’ which didn’t provide much help and the

cause was not obvious. After a lot of research and trial and error I

found some answers.

Regarding the first issue, I found this page on MSDN which also show’s

how to create a switch statement.

http://msdn2.microsoft.com/en-us/library/csx7wsz2(vs.80).aspx. The

solution is to create a Label object and MakeLabel method when Emitting

the IL.

Label endOfMethod = il.DefineLabel();
...
il.Emit(OpCodes.Br_S, endOfMethod);
il.MarkLabel(endOfMethod);

  The above will create IL like this:

IL_0017:  br.s       IL_001
IL_0019:  ldloc.1

  The second problem maybe should have been obvious, but most of what I

  read didn’t cover this. If you need to store something you need to

  create local storage before trying to store objects there. Not doing

  this will result in a System.InvalidProgramException. You need to

  create the storage with the il.DeclareLocal method passing in the Type

  of the object you will store there.

il.DeclareLocal(stringBuilderType);
il.DeclareLocal(typeof(string));

  The above will create IL like:

.locals init (class [mscorlib]System.Text.StringBuilder V_0,
              string V_1)

  Working sample command line application (.net2.0) flie – Program.cs.txt (2.45 KB)