[petsc-dev] #define FORTRANNULLFUNCTION(a) (((void(*)(void))(PETSC_UINTPTR_T)a) == PETSC_NULL_FUNCTION_Fortran)

[Barry Smith]

  Jed,

    It seems this PETSC_UINTPTR_T here is allowing one to cast a void * to a 
function pointer without generating a warning/error? Is this correct code? Why 
does it even work?

    I’m trying to get rid of the last of the "casting object pointer to 
function pointer" warning messages out of PETSc but still get a truck load with 

#define CHKFORTRANNULLFUNCTION(a)  \
  if (FORTRANNULLSCALAR(a) || FORTRANNULLDOUBLE(a) || FORTRANNULLREAL(a) || 
FORTRANNULLINTEGER(a) || FORTRANNULLOBJECT(a)) { \
    
PetscError(PETSC_COMM_SELF,__LINE__,"fortran_interface_unknown_file",__FILE__,PETSC_ERR_ARG_WRONG,PETSC_ERROR_INITIAL,
 \
    "Use PETSC_NULL_FUNCTION"); *ierr = 1; return; } \
  else if (FORTRANNULLFUNCTION(a)) { a = NULL; }


because each of the FORTRANNULLXXX() tests  cast the function pointer a to an 
object pointer. Can I instead use the PETSC_UINTPTR_T  trick to cast the object 
pointers
 like PETSC_NULL_INTEGER_Fortran to function pointers and compare them to 
eliminate all the warnings?

    Thanks

   Barry