alignment/padding when mixing C struct and fortran 90 derived type

[burlen <burlen at apollo dot sr dot unh dot edu>]

Hi all,

currently I have some C code that will call a fortran 90 subroutine. In 
the C portion I have defined:

struct record
{
 int id;
 int dataLen;
 int *pFile;
 double *data;
 int ofs;
};

while in the fortran code I have defined:

module GGCM
type  record
   integer :: id
   integer :: dataLen
   integer, pointer :: pFile
   real*8, pointer :: data
   integer :: ofs
   end type record
contains
end module

From a C code I will declare an instance of record, initialize it and 
call a fortran subroutine which is defined like so

subroutine manipulateCStruct( kot )
 use  GGCM
 implicit none

 type(record) :: kot

 kot%id = kot%ofs
 kot%pFile = kot%ofs ! this should modify file which is in main.cpp
 kot%ofs = 128

 end subroutine

These will be compiled and linked using gcc, and gfortran.  All is fine, 
and works as I'd like with out compiler optimization. My question is 
will I be safe passing above struct when compiler optimizations are 
enabled? I have the intuition that so far as the compile lines use the 
identical optimization flags, then all will be OK. But I'd like to 
confirm if possible gfortran and gcc use same alignment/padding 
optimizations.

Thanks in advance
Burlen