/*  Note that struct foo is opaque (never defined) in this file.  This    is allowed by C since this file does not reference any members of    the structure.  The debugger needs to be able to associate this    opaque structure definition with the full definition in another    file.*/struct foo *foop;extern struct foo *getfoo ();#ifdef PROTOTYPESextern void putfoo (struct foo *foop);#endifint main (){#ifdef usestubs    set_debug_traps();    breakpoint();#endif    foop = getfoo ();    putfoo (foop);    return 0;}