in c#, i have intptr win32 wndproc. syntax job it?

i'm subclassing internal window (the correct control combobox...)

oldwndproc = setwindowlong(handleofcbeditcontrol, gwl_wndproc, newwndproc);

in subclassing wndproc, i'll have formula this, right, nonetheless i can't figure out syntax job oldwndproc.

    int mywndproc(int msg, int wparam, int lparam)
    {
         (msg.m ==  something i'm prying in...)
         {
              relapse something special
         }
         else
         {
              relapse outcome oldwndproc  <<<<   does feeling like?***
         }

    }

edit: "subclassing" doubt refers win32 api meaning, c#. subclassing here doesn't meant vital .net bottom category behavior. means explanation win32 your duty pointer instead windows tide callback. zero inheritence c#.