//引入命名空间
using System;
using System.Threading;
using System.Reflection;
using System.Reflection.Emit;
class ILLabelDemo {
public static Type BuildAdderType() {
AppDomain myDomain = Thread.GetDomain();
AssemblyName myAsmName = new AssemblyName();
myAsmName.Name = "AdderExceptionAsm";
AssemblyBuilder myAsmBldr = myDomain.DefineDynamicAssembly(myAsmName,
AssemblyBuilderAccess.Run);
ModuleBuilder myModBldr = myAsmBldr.DefineDynamicModule("AdderExceptionMod");
TypeBuilder myTypeBldr = myModBldr.DefineType("Adder");
Type[] adderParams = new Type[] {typeof(int), typeof(int)};
// This method will add two numbers which are 100 or less. If either of the
// passed integer vales are greater than 100, it will return the value of -1.
MethodBuilder adderBldr = myTypeBldr.DefineMethod("DoAdd",
MethodAttributes.Public |
MethodAttributes.Static,
typeof(int),
adderParams);
ILGenerator adderIL = adderBldr.GetILGenerator();
// In order to successfully branch, we need to create labels
// representing the offset IL instruction block to branch to.
// These labels, when the MarkLabel(Label) method is invoked,
// will specify the IL instruction to branch to.
Label failed = adderIL.DefineLabel();
Label endOfMthd = adderIL.DefineLabel();
// First, load argument 0 and the integer value of "100" onto the
// stack. If arg0 > 100, branch to the label "failed", which is marked
// as the address of the block that loads -1 onto the stack, bypassing
// the addition.
adderIL.Emit(OpCodes.Ldarg_0);
adderIL.Emit(OpCodes.Ldc_I4_S, 100);
adderIL.Emit(OpCodes.Bgt_S, failed);
// Now, check to see if argument 1 was greater than 100. If it was,
// branch to "failed." Otherwise, fall through and perform the addition,
// branching unconditionally to the instruction at the label "endOfMthd".
adderIL.Emit(OpCodes.Ldarg_1);
adderIL.Emit(OpCodes.Ldc_I4_S, 100);
adderIL.Emit(OpCodes.Bgt_S, failed);
adderIL.Emit(OpCodes.Ldarg_0);
adderIL.Emit(OpCodes.Ldarg_1);
adderIL.Emit(OpCodes.Add_Ovf_Un);
adderIL.Emit(OpCodes.Br_S, endOfMthd);
// If this label is branched to (the failure case), load -1 onto the stack
// and fall through to the return opcode.
adderIL.MarkLabel(failed);
adderIL.Emit(OpCodes.Ldc_I4_M1);
// The end of the method. If both values were less than 100, the
// correct result will return. If one of the arguments was greater
// than 100, the result will be -1.
adderIL.MarkLabel(endOfMthd);
adderIL.Emit(OpCodes.Ret);
return myTypeBldr.CreateType();
}
public static void Main() {
Type adderType = BuildAdderType();
object addIns = Activator.CreateInstance(adderType);
object[] addParams = new object[2];
Console.Write("Enter an integer value: ");
addParams[0] = (object)Convert.ToInt32(Console.ReadLine());
Console.Write("Enter another integer value: ");
addParams[1] = (object)Convert.ToInt32(Console.ReadLine());
Console.WriteLine("---");
int adderResult = (int)adderType.InvokeMember("DoAdd",
BindingFlags.InvokeMethod,
null,
addIns,
addParams);
if (adderResult != -1) {
Console.WriteLine("{0} + {1} = {2}", addParams[0], addParams[1],
adderResult);
} else {
Console.WriteLine("One of the integers to add was greater than 100!");
}
}
}
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