Re: [Chicken-users] return a float from foreign function

[Zbigniew]

Hello,

This is not a problem with Chicken nor with your use of float as
return type (float means float in Chicken, not double).

The problem is that you didn't provide a C prototype for your external
function.  This is a C issue, as you will see if you write a simple C
program:

$ cat > test.c <<EOF
#include <stdio.h>
/* float baz(int); */  /* look ma, no prototype */
int main(void) { printf("baz 42: %f\n", baz(42)); }
EOF
$ gcc -o test test.c impl.c
$ ./test
$ baz 42: 0.000000

Now uncomment the prototype and it works correctly.

To fix in your case, add the following to the top of callit.scm.

#> float baz(int); <#

Under normal use, of course, you would use
#> #include <impl.h> #<

Or use foreign-lambda* and include the code inline.

On 8/27/06, Shawn Rutledge <address@hidden> wrote:
> impl.c:
>
> #include <math.h>
>
> float baz(int i)
> {
>         return (((float)i) / 15.2);
> }
>
> callit.scm:
>
> (define baz (foreign-lambda float "baz" int))
> (display baz)
> (display (baz 42))
>
> csc callit.scm impl.c
>
> ./callit
> #<procedure (baz a25)>42.0
>
> Change impl.c to make sure it's being called at all:
>
> #include <math.h>
> #include <stdio.h>
>
> float baz(int i)
> {
>         printf("baz given %d\n", i);
>         return (((float)i) / 15.2);
> }
>
> ./callit
> #<procedure (baz a25)>baz given 42
> 13.0
>
> This is with chicken 2.2 and I think 2.3 also has similar problems.  I
> can try 2.41 when it gets done building.