Ian Lance Taylor wrote:
burlen <burlen.loring@xxxxxxxxx> writes:
Ian Lance Taylor wrote:
burlen <burlen.loring@xxxxxxxxx> writes:
When calling a c function from a fortran 90 program with members of a
user defined types for output arguments of the called subroutine the
user defined types aren't being modified as they should be (according
to my understanding).
When you call a C function, you get the C rules. It doesn't matter
whether you are calling it from Fortran or not. In C, a modification
of an argument is not reflected back to the caller.
Ian
In my understanding, Fortran unless otherwise instructed is supposed
to pass by address. In the c function modifying the data pointed to
should do just that, and be visible to the caller. What I don't
understand is why passing the member of a user defined type behaves as
if it's passed by value in this case, while passing the corresponding
native type is passed by address and works as expected.
I think you are going to have to provide an example.
If you write a C function
void foo(int i) { i = 1; }
then the parameter is not going to change in the caller. That's just
how C works. There is no reasonable way to change that.
Ian
True. But when you're mixing fortran and c you don't write your c
function that way, because fortran passes by address. I don't know if
it's mandated by a standard or not, but that's just how it's implemented
in my experience. I have used mixed language programming with gnu,
intel, and portland group. This is my first attempt at making use of the
so called object oriented features of fortran 90 .
For example your function would have to be written as follows:
/* start of c code */
void foo_(int *i)
{
(*i)=1;
}
/* end of c code */
This can be called from a fortran program as follows:
! start of fortran code
program main
integer i
i=0
call foo(i)
write(0,*)i
end program
! end of fortran code
compile like this:
$ gcc ccode.c -c -o ccode.o
$ gfortran fcode.f90 ccode.o -o fcode
$ ./fcode
1
