C#: Getting size of a value-type variable at runtime?

Question

I know languages such as C and C++ allow determining the size of data (structs, arrays, variables...) at runtime using sizeof() function. I tried that in C# and apparently it does not allow putting variables into the sizeof() function, but type defintions only (float, byte, Int32, uint, etc...), how am I supposed to do that?

Practically, I want this to happen:

int x; Console.WriteLine(sizeof(x));   // Output: 4 

AND NOT:

Console.WriteLine(sizeof(int)); // Output: 4 

I'm sure there's some normal way to get the size of data at runtime in C#, yet google didn't give much help.. Here it is my last hope

Answer 1

Following on from Cory's answer, if performance is important and you need to hit this code a lot then you could cache the size so that the dynamic method only needs to be built and executed once per type:

int x = 42; Console.WriteLine(Utils.SizeOf(x));    // Output: 4  // ...  public static class Utils {     public static int SizeOf<T>(T obj)     {         return SizeOfCache<T>.SizeOf;     }      private static class SizeOfCache<T>     {         public static readonly int SizeOf;          static SizeOfCache()         {             var dm = new DynamicMethod("func", typeof(int),                                        Type.EmptyTypes, typeof(Utils));              ILGenerator il = dm.GetILGenerator();             il.Emit(OpCodes.Sizeof, typeof(T));             il.Emit(OpCodes.Ret);              var func = (Func<int>)dm.CreateDelegate(typeof(Func<int>));             SizeOf = func();         }     } }