Re: data types

[Nigel Wade <nmw(at)ion.le.ac.uk>]

graham_wilson@my-deja.com wrote:
> 
> I'm trying to compile a short listing of data types for converting
> between F77, C, and IDL.
> 
> Below is a listing of what I have but note that I have not filled in all
> of the IDL column.  Any and all comments/help is appreciated and my
> appologies to those of you who don't use fixed fonts for reading mail.
> 
> F77 type            C type                    IDL type       Size
> (bytes)
> -----------------------------------------------------------------------
> byte x              char x                    byte             1
> character x         char x                    byte             1
> character*n x       char x[n]                 bytearr(n)       n
> 
> complex x           struct {float r, i;} x    ?                8
> complex*8 x         struct {float r, i;} x    ?                8
> double complex x    struct {float dr, di;} x  ?                16
> complex*16 x        struct {float dr, di;} x  ?                16
> complex*32 x        struct {float dr, di;} x  ?                32
> 
> double precision x  double                    double           8
> real x              float x                   float            4
> real*4 x            float x                   float            4
> real*8 x            double x                  double           8
> real*16 x           long double x             ?                16
> 
> integer x           int x                     long             4
> integer*2 x         short x                   fix              2
> integer*4 x         int x                     long             4
> integer*8 x         long long int x           ?                8
> 
> logical x           int x                     long             4
> logical*1           char x                    byte             1
> logical*2           short x                   fix              2
> logical*4           int x                     long             4
> logical*8           long long int x           ?                8
> 
> NB: I'm assuming that there are no fancy compiling options given to
> change the alignment or the default sizes.
> 
> Such a list would be useful as an appendix in one of those IDL books we
> keep hearing about (better still if it had the byte alignment for
> sparc/intel/powerpc/dec/mips...)  :p
> 
> Sent via Deja.com
> http://www.deja.com/

IDL's COMPLEX type will match a C struct {float r; float i; } provided
a C float is the same as a float in IDL and there is no padding inserted
by the C compiler. DCOMPLEX should match struct { double r; double i}.
AFAIK IDL does not have a 64 bit float. It does now have LONG64 which 
should match your integer*8 and long long int.

Your double complex, complex*16 and complex*32 would appear to be 
inconsistent with your normal complex. Two floats cannot be 8, 16 and 32
bytes!

You don't say which platform your table is for. As I am sure you are
aware
ANSI C places very few restrictions on the sizes of the basic types, and
no restriction on padding within structures. So you need to be very 
specific in saying for what platform/compiler/compiler-defaults the 
values are valid.
 
-- 
-----------------------------------------------------------
Nigel Wade, System Administrator, Space Plasma Physics Group,
            University of Leicester, Leicester, LE1 7RH, UK 
E-mail :    nmw@ion.le.ac.uk 
Phone :     +44 (0)116 2523568, Fax : +44 (0)116 2523555