Re: Returning values from C function?

[erik dot edelmann at iki dot fi]

On Tue, Dec 26, 2006 at 12:19:45PM -0800, Steve Kargl wrote:
> On Tue, Dec 26, 2006 at 03:05:37PM -0500, Jeremy C wrote:
> > Greetings! I am able to make this function in C:
> > 
> > int hello_(int *times, char *to_who) {
> >  for (int idx=0; idx<*times; idx++) {
> >    printf("Hello, %s!\n", to_who);
> >  }
> > 
> >  return 10;
> > }
> 
> #include <stdio.h>  /* Add missing header files.  */
> int
> hello_ (int *times, char *to_who)
> {
>   int idx;  /*  Fix warning.  */
> 
>   for (idx = 0; idx < *xtimes; idx++)
>     printf("Hello, %s!\n", to_who);
>  
>   return 10;
> }
> 
> > 
> > integer :: a
> > 
> > print *, hello(10, "Me")
> > 
> > 
> 
> program hello_me
>   integer, external :: hello
>   print *, hello(10, "Me")
> end program hello_me.
> 
> > I get "Hello, Me!" printed on the screen 10 times as expected, but it
> > prints what seems like a pointer address.
> 
> The above works for me.

One thing that could go wrong is that the C function 'printf' expects
strings to be NULL terminated (i.e., it will continue to print characters
until it finds a '\0'-character).  In fortran, however, strings are not in
general NULL terminated.  Printing a string in C code that was passed from
Fortran code can therefore sometimes result in some extra garbage being
printed.


        Erik