| Re: Calling fortran under unix [message #7103 is a reply to message #7101] |
Wed, 02 October 1996 00:00  |
korpela
Messages: 59
Registered: September 1993
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Member |
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In article <32523466.41C6@mod5.ag.rl.ac.uk>,
Simon Williams <williams@mod5.ag.rl.ac.uk> wrote:
> I gather that the CALL_EXTERNAL interface is rather different
> under Unix, and that I might have to write some sort of
> intermediate "wrapper" between the idl and the fortran.
>
> I would be very grateful if anyone could show me how to do
> it for a simple example:
>
> subroutine simple(a,b,c)
>
> integer a,b,c
>
> c=a+b
>
> end
You'll have to write a C wrapper that calls your fortran subroutine.
Here's an example that may work on your above example.
------------------------------------------------------------ --------------
/* here's the prototype for the fortran function */
void simple_(int *a, int *b, int *c);
int wrapper(int argc, void *argv[])
{
int *a, *b, *c;
/* check the number of arguments */
if (argc == 3) {
a=(int *)argv[0];
b=(int *)argv[1];
c=(int *)argv[2];
simple_(a,b,c);
return(0);
} else {
return(-1);
}
}
------------------------------------------------------------ ---------------
you'd hace to link the wrapper function and the fortran function into the
same shared library. Under SunOs the commands would be...
% gcc -Wall -fpic -c wrapper.c
% f77 -PIC -c simple.f
% ld -o simple.so -assert pure-text simple.o wrapper.o -lF77
Under your unix they may be different.
The call_external statement would be:
error_code=call_external('simple.so','wrapper',a,b,c)
------------------------------------------------------------ ---------------
The general rules for linking C and Fortran are
1) Most varieties of fortran append an underscore to function names.
The fortran function hello() becomes the C function hello_()
2) Fortran subroutine and function parameters are passed as pointers.
subroutine garbage(a,b,c) INTEGER*4 a, REAL b, INTEGER*2 c
becomes void garbage_(long *a, float *b, short *c)
3) Watch your types! "integer" is not necessarily "int". In your fortran
code use integer*2 and integer*4 in the C code use short and long.
Use real and double precision in fortran. float and double in C.
None of the above is guaranteed to work, but it's a starting point.
4) Fortran arrays are passed as a pointer to the first element of the array
subroutine garbage(a,b,c) INTEGER*4 a(100), REAL B(100), INTEGER*2 c(100)
becomes void garbage_(long *a, float *b, short *c)
5) To avoid all these problems, skip fortran and move straight to C.
Eric
--
Eric Korpela | An object at rest can never be
korpela@ssl.berkeley.edu | stopped.
<a href=" http://www.cs.indiana.edu/finger/mofo.ssl.berkeley.edu/korpe la/w">
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