The "trivial example" of a closure in libffi info does not work

[Andrew Haley <aph at redhat dot com>]

The example in the libffi doc does not work.  It uses the wrong types,
and will not compile:


trivial.c: In function 'main':
trivial.c:21:3: warning: passing argument 2 of 'ffi_closure_alloc' from incompatible pointer type [enabled by default]
   closure = ffi_closure_alloc(sizeof(ffi_closure), &bound_puts);
   ^
In file included from /usr/include/ffi.h:10:0,
                 from trivial.c:2:
/usr/include/ffi-ppc64.h:318:7: note: expected 'void **' but argument is of type 'int (**)(char *)'
 void *ffi_closure_alloc (size_t size, void **code);
       ^
trivial.c:34:8: warning: passing argument 3 of 'ffi_prep_closure_loc' from incompatible pointer type [enabled by default]
        stdout, bound_puts) == FFI_OK)
        ^
In file included from /usr/include/ffi.h:10:0,
                 from trivial.c:2:
/usr/include/ffi-ppc64.h:328:1: note: expected 'void (*)(struct ffi_cif *, void *, void **, void *)' but argument is of type 'void (*)(struct ffi_cif *, ffi_arg *, void **, struct FILE *)'
 ffi_prep_closure_loc (ffi_closure*,
 ^

I have appended a corrected version.

Andrew.


#include <stdio.h>
#include <ffi.h>

/* Acts like puts with the file given at time of enclosure. */
void puts_binding(ffi_cif *cif, void *ret, void* args[],
                  void *stream)
{
  *(ffi_arg *)ret = fputs(*(char **)args[0], (FILE *)stream);
}

typedef int (*puts_t)(char *);

int main()
{
  ffi_cif cif;
  ffi_type *args[1];
  ffi_closure *closure;

  void *bound_puts;
  int rc;

  /* Allocate closure and bound_puts */
  closure = ffi_closure_alloc(sizeof(ffi_closure), &bound_puts);

  if (closure)
    {
      /* Initialize the argument info vectors */
      args[0] = &ffi_type_pointer;

      /* Initialize the cif */
      if (ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 1,
                       &ffi_type_sint, args) == FFI_OK)
        {
          /* Initialize the closure, setting stream to stdout */
          if (ffi_prep_closure_loc(closure, &cif, puts_binding,
                                   stdout, bound_puts) == FFI_OK)
            {
              rc = ((puts_t)bound_puts)("Hello World!");
              /* rc now holds the result of the call to fputs */
            }
        }
    }

  /* Deallocate both closure, and bound_puts */
  ffi_closure_free(closure);

  return 0;
}