| Re: passing idl structures in call_external ? [message #6028] |
Wed, 10 April 1996 00:00 |
Robert Cannon
Messages: 5
Registered: February 1996
|
Junior Member |
|
|
Christian Soelle wrote:
>
> As the subject already says, does anybody know how to pass idl-structures
> to a C-function using CALL_EXTERNAL. I couldn't find anything in the help
> nor in the example programs supplied.
>
I don't know anything official, but as the prefious reply said, they
generally turn out to be alligned the same way between c and IDL.
I use the routine below (structtoc) to produce a c header file to
declare the structure once I have defined it in IDL.
I hope it is of some use,
Robert
Neuroscience Research Group
School of Biologial Sciences
Southampton, UK SO16 7PX
rcc@hera.neuro.soton.ac.uk
FUNCTION structname, a
hhh = gethelp ('a')
hh = hhh(0)
fa = strpos (hh, '->')
fb = strpos (hh, 'Arra')
nn = strmid (hh, fa+2, fb - (fa+2) )
IF strlen (nn) EQ 2 THEN nn = 'annon'
return, strlowcase (nn)
END
PRO structtoc, strin
; given an idl structure str, write a c
;header file declaring this struture
str = strin
; types, as returned by size
types = ['undefined ', $ ; 0
'byte ', $ ; 1
'short int ', $ ; 2
'int ', $ ; 3
'float ', $ ; 4
'double ', $ ; 5
'complex ', $ ; 6
'string ', $ ; 7
'struct ', $ ; 8
'dcomplex ']
nt = n_tags (str)
tn = strlowcase (tag_names (str))
nel = n_elements (str)
IF nel gt 1 THEN BEGIN
; str is an array of structures
subs = str(0)
structtoc, subs
END ELSE BEGIN
; check to see if it contains any
structures
FOR i = 0, nt-1 DO BEGIN
sf = size (str.(i))
sr = reverse (sf)
IF sr(1) EQ 6 OR sr(1) EQ 7 OR sr(1) EQ 10 OR sr(1) EQ 0 THEN
BEGIN
message, 'cant do this structure - dont like types'
END
IF sr(1) EQ 8 THEN BEGIN
subs = str.(i)
structtoc, subs
END
END
stnm = structname (str)
print, 'typedef struct '
print, '{'
FOR i = 0, nt-1 DO BEGIN
sf = size (str.(i))
sr = reverse (sf)
vardec = types (sr(1))
IF sr(1) EQ 8 THEN BEGIN
; get the name of the structure
a = str.(i)
vardec = structname (a)
END
IF sf(0) EQ 0 THEN BEGIN
line = vardec + tn(i) + ';'
END ELSE BEGIN
IF sf(0) GT 1 THEN BEGIN
print, '/* following is an idl multidimensional
array: '
print, fix(sf(0)), ' dims: ', fix(sf(1:sf(0))), '*/'
END
line = vardec + tn(i) + $
'[' + strtrim(string(sr(0)), 2) + ']' + ';'
END
print, ' ' + line
END
print, '} ' + stnm + ';'
print
print
END
END
|
|
|
|
| Re: passing idl structures in call_external ? [message #6043 is a reply to message #6028] |
Thu, 04 April 1996 00:00  |
hahn
Messages: 108
Registered: November 1993
|
Senior Member |
|
|
csoelle@msfd12.gwdg.de (Christian Soelle ) wrote:
> As the subject already says, does anybody know how to pass idl-structures
> to a C-function using CALL_EXTERNAL. I couldn't find anything in the help
> nor in the example programs supplied.
> Did I miss something ? Is there anyone who can shed some light on this
> problem ?
See page 3-5 in IDL Advanced Development Guide, version 4.
Hope this helps
Norbert
Remember: IDL user's meeting on April 18th an 19th in Augsburg,
Germany. Have you registered?
> Regards,
> Christian
> --
> ____________________________________________________________
> | |
> | Christian Soeller email: csoelle@msfd12.gwdg.de |
> | |
> | Max-Planck-Institut for Fluid Dynamics |
> | Bunsenstrasse 10 |
> | 37073 Goettingen / Germany |
> ____________________________________________________________
|
|
|
|
| Re: passing idl structures in call_external ? [message #6045 is a reply to message #6043] |
Thu, 04 April 1996 00:00 |
David Foster
Messages: 341
Registered: January 1996
|
Senior Member |
|
|
csoelle@msfd12.gwdg.de (Christian Soelle ) wrote:
>
>
> As the subject already says, does anybody know how to pass idl-structures
> to a C-function using CALL_EXTERNAL. I couldn't find anything in the help
> nor in the example programs supplied.
Most wouldn't consider this a problem, because an IDL structure
doesn't mean much in the context of a C function. The first
problem is how to declare the pointer argument in the C
function. Then you have to figure out how to reference the
structures using pointer offsets, and I'm not sure this would
work (the alignment might create problems). I hope someone
more familiar with this can address these problems.
I think you would be better off passing information to your
C routine using individual arguments.
Dave Foster
foster@bial1.ucsd.edu
|
|
|
|
| Re: passing idl structures in call_external ? [message #6047 is a reply to message #6043] |
Thu, 04 April 1996 00:00 |
rivers
Messages: 228
Registered: March 1991
|
Senior Member |
|
|
In article <CSOELLE.96Apr4151011@msfd12.gwdg.de>, csoelle@msfd12.gwdg.de (Christian Soelle ) writes:
>
> As the subject already says, does anybody know how to pass idl-structures
> to a C-function using CALL_EXTERNAL. I couldn't find anything in the help
> nor in the example programs supplied.
>
The last time I looked, the means by which structures are passed was
intentionally not documented, presumably so that RSI would be free to change it
in the future.
However, I know by experience that IDL presently passes structures just like
you would expect, i.e. it passes the address of the start of the structure. All
structure elements except strings are contained in the structure itself, i.e.
the structure contains the value, not a pointer. Strings are different:
the structure contains either the descriptor or the address of the descriptor
(I forget).
I routinely pass structures to CALL_EXTERNAL, but I do so at my own risk,
since it is not guaranteed to be done the same way in future versions of IDL.
I have found that the structures will contain padding to keep the members
aligned on natural boundaries. The C compiler will normally do this on the
structures in your CALL_EXTERNAL code as well, so it has not been a problem.
____________________________________________________________
Mark Rivers (312) 702-2279 (office)
CARS (312) 702-9951 (secretary)
Univ. of Chicago (312) 702-5454 (FAX)
5640 S. Ellis Ave. (708) 922-0499 (home)
Chicago, IL 60637 rivers@cars3.uchicago.edu (Internet)
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
