I have problem. This is my code:
var method = new DynamicMethod("dummy", null, Type.EmptyTypes);
var g = method.GetILGenerator();
g.DeclareLocal(typeof(int));
Label inequality = g.DefineLabel();
Label equality = g.DefineLabel();
Label end = g.DefineLabel();
g.Emit(OpCodes.Ldstr, "string");
g.Emit(OpCodes.Ldstr, "string");
g.Emit(OpCodes.Call, typeof(String).GetMethod("op_Equality", new Type[]{typeof(string), typeof(string)}));
g.Emit(OpCodes.Stloc_0);
g.Emit(OpCodes.Ldloc_0);
g.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new Type[]{typeof(int)}));
g.Emit(OpCodes.Ldloc_0);
g.Emit(OpCodes.Ldc_I4_1);
g.Emit(OpCodes.Ceq);
g.Emit(OpCodes.Brtrue_S, equality);
g.Emit(OpCodes.Brfalse_S, inequality);
g.MarkLabel(inequality);
g.Emit(OpCodes.Ldstr, "Specified strings are different.");
g.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new Type[]{typeof(string)}));
g.Emit(OpCodes.Br_S, end);
g.MarkLabel(equality);
g.Emit(OpCodes.Ldstr, "Specified strings are same.");
g.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }));
g.Emit(OpCodes.Br_S, end);
g.MarkLabel(end);
g.Emit(OpCodes.Ret);
var action = (Action)method.CreateDelegate(typeof(Action));
action();
This is my result:
1
Specified strings are different.
But why is output wrong? Ceq instruction is comparing 1 as result from op_Equation and 0 which is on the top of stack. And 1 not equals 0. So why it is? Where is error? Please help me.
After g.Emit(OpCodes.Brtrue_S, inequality);
, you need to jump to the "equality" statement manually. Else it will execute the next instruction anyway. So you'll need to insert the following line after it:
g.Emit(OpCodes.Br_S, equality);
Also, it doesn't make sense to jump to the label equality
when it is declared as the next instruction anyway. So remove that.
so the section will look like this:
g.Emit(OpCodes.Ceq);
g.Emit(OpCodes.Brtrue_S, inequality); // if true goto inequality
g.Emit(OpCodes.Br_S, equality); // else goto equality
g.MarkLabel(inequality);
g.Emit(OpCodes.Ldstr, "Specified strings are different.");
g.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new Type[]{typeof(string)}));
g.Emit(OpCodes.Br_S, end); // goto end
g.MarkLabel(equality);
g.Emit(OpCodes.Ldstr, "Specified strings are same.");
g.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }));
g.MarkLabel(end);
g.Emit(OpCodes.Ret);