| Re: Help on calling Fortran routines from IDL under linux [message #36583] |
Wed, 08 October 2003 05:38  |
Nigel Wade
Messages: 286
Registered: March 1998
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Senior Member |
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David Green wrote:
> For the past few days i have been trying to call basic fortran
> routines from IDL (IDL 6.0 and Gentoo Linux on a PC). First i tried
> using the CALL_EXTERNAL approach using both fortran and C wrappers as
> shown in the IDL documentation however the output i was getting from
> the sum_array example was incorrect. Here is what i did first:
>
> ------------------------------------------------------------ ---------
> test_call_external.pro - the IDL calling routine
> ------------------------------------------------------------ ---------
> pro test_call_external
>
> x = [1.0,2.0,3.0]
> sum = 0.0
> n = n_elements(x)
> s = call_external('/home/david/PhD/Fortran/sum_array.so',
> 'sum_array', $
> x, n, sum)
> print, s
> help, s
>
> end
>
> ------------------------------------------------------------ ---------
> sum_array.c - the C wrapper as in the IDL documentation
> ------------------------------------------------------------ ---------
> #include <stdio.h>
>
> void sum_array(int argc, void *argv[])
> {
> extern void sumd_(); /* Fortran Routine */
> int *n;
> float *s, *f;
>
> f = (float *) argv[0]; /* Array pntr */
> n = (int *) argv[1]; /* Get # of elements */
> s = (float *) argv[2]; /* Pass back result a parameter */
>
> sumd_(f, n, s); /* Compute Sum */
> }
>
> ------------------------------------------------------------ ---------
> sumd.f - the Fortran routine as in the documentation
> ------------------------------------------------------------ ---------
> SUBROUTINE sumd(array, n, sum)
> INTEGER*4 n
> REAL*4 array(n), sum
>
> sum=0.0
> DO i=1,n
> sum = sum + array(i)
> ENDDO
>
> RETURN
> END
>
>
> I compiled both the sumd.f and sum_array.c files to objects then
> linked them together into a shared object (sum_array.so) using gcc (i
> think, i'm a gcc ultra newbie) as follows:
>
> gcc -c sumd.f
> gcc -c sum_array.c
> gcc -shared -o sum_array.so sumd.o sum_array.o
>
> However, when i compile and run test_call_external i get the output:
>
> -1073746820
> S LONG = -1073746820
>
> This, i don't understand, so i figured i'd try the fortran wrapper
> like this...
>
> ------------------------------------------------------------ ---------
> dave.f - the Fortran routine as in the documentation
> ------------------------------------------------------------ ---------
> SUBROUTINE SUM_ARRAY(argc, argv) !Called by IDL
> INTEGER*4 argc, argv(*) !Argc and Argv are integers
>
> j = LOC(argc) !Obtains the number of arguments (argc)
> !Because argc is passed by VALUE.
>
> CALL SUM_ARRAY1(%VAL(argv(1)), %VAL(argv(2)), %VAL(argv(3)))
> RETURN
> END
>
> SUBROUTINE SUM_ARRAY1(array, n, sum)
> INTEGER*4 n, test
> REAL*4 array(n), sum
>
> sum=0.0
> DO i=1,n
> sum = sum + array(i)
>
> ENDDO
> RETURN
> END
>
> I compiled this with gcc as (to get the shared object dave.so)
>
> gcc -w -shared -o dave.so dave.f
>
> and then run the following idl program...
>
> ------------------------------------------------------------ ---------
> test_call_external2.pro - idl calling routine
> ------------------------------------------------------------ ---------
> pro test_call_external
>
> x = [1.0,2.0,3.0]
> sum = 0.0
> n = n_elements(x)
> s = call_external('/home/david/PhD/Fortran/dave.so', 'sum_array__', $
> x, n, sum)
> print, s
> help, s
>
> end
Hmm, shouldn't that be 'print, sum'? Your C wrapper puts the sum in the 3rd
parameter, argv[2].
Also, your C wrapper return type is void, so s in IDL will have no value.
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