Call C function from Fortran 1

[zhoubinbin]

Hi, anybody can help me!!

I want to call a C function from a Fortran code, For example, I have a C function void ABC(int *x) saved in C_file.c, I want to call this ABC from a Fortran code, such as

Integer X
Call ABC_(X)

which is in F_file.f

So How to link and compile and run this
Fortran code.

Thanks

Binbin

 

[CaKiwi]

The details of how to do this depend on the system and compilers you are using, but in general you would compile the C and Fortran files into separate objects and link them in exactly the same way as you would link 2 objects created with either C or Fortran. Some systems append an underscore to the end of Fortran subroutine names so in your example you may need to declare your C subroutine

void ABC_(int *x)

and call it in Fortran

call ABC(x)

If you are going to port this code to several systems it is a good idea to use defines in a C header file to handle this problem e.g.

#ifdef SGI
#define ABC ABC_
#endif
void ABC(int *x)

Also remember that all arguments are passed by reference in Fortran as you showed in your example.

Let me know if you have any more questions.

CaKiwi

 

[zhoubinbin]

Hi, CaKiwi:

Thanks.

I use HP-UX. Now I found a way to link these object by using +ppu flag, which appends a underscore behind ABC, so that
f77 compiler can find ABC_().
In this case, should be ABC_(int *X), in
Fortran code, should be CALL ABC(X). In my previous post, order was wrong.

Binbin

 

[CG101]

G'day,

I have a program written in fortran 77 (test.f), in which I am trying to call a handful of C subroutines, written in addins.c. I am new to C, Fortran, compiling and programming in general, so I have a number of what may be simplistic questions...

Currently my fortran program just contains the command:
call subroutine(a,b,c)

How do I tell the program where this subroutine is?
Do I need external subroutine !$PRAGMA (addins.c),
or include addins.c,
or something similar?
And do I need to declare the subroutine as int subroutine or something prior to calling it?

In the C program, I currently just have the subroutines, and no main(). Do I need to include main()?

I think that the problem lies in compiling and then linking the two bits of code. How do I do this?
I am working on SunOS 5.8, using compilers cc (no gcc), and f77.
How can I compile the bits of code individually (if this is required) - as errors are given due to fortran not recgnising the C subroutines, and C not having a main().
Then how do I combine the two bits?

Thanks in advance,
CG

 

[CaKiwi]

Here's a simple example

/* ------ C file addins.c ------ */

#define csub csub_
csub(int *i4)
{
*i4 = 1;
}

C ------ fortran file fc.f ------

program fc

integer*4 i4/0/

call csub(i4)

print *, 'i4 = ',i4

end

#Compile the C file with the -c option to create an object

cc -c addins.c

# Compile the fortran file and link with the C object

f77 fc.f addins.o

# run the executable

a.out

CaKiwi

"I love mankind, it's people I can't stand" - Linus Van Pelt

 

[CG101]

Thanks, i've been banging my head against that particular brick wall for a while. Didn't realise before that you could compile without trying to make an executable (ie the cc -c option).

 

[wenfangtan]

I have one more question:
If in the c funtion, I defined some macro and enum, and my c funtion call use these enum as argument, How can i call this function in fortran?
example:
in c:
typedef enum
{ X =0,
Y = 1
}FORMAT
...
void foo_(FORMAT myformat);
thanks a lot.
tan

 

[CaKiwi]

You could probably pass it as an integer array, although if it is a global definition as your example implies, you would have to redefine it in fortran. The best way might be to write a function in C that could be called from fortran and would pass the appropriate enum to your foo_() function.

CaKiwi

"I love mankind, it's people I can't stand" - Linus Van Pelt