how to define a "ffi_type" for a struct with inlined arrays for libffi

array.c

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

/* The struct with inlined arrays */
struct test {
  int array[5];
  char str[6];
};

/* The function to FFI invoke */
struct test fn (struct test test, int input) {
  int i;
  for (i = 0; i < 5; i++) {
    printf("test.array[%d]: %d\n", i, test.array[i]);
  }
  printf("test.str as string: %s\n", &test.str[0]);
  printf("int input: %d\n", input);
  return test;
}


int main () {
  ffi_cif cif;
  ffi_type test_struct_type;
  ffi_type *arg_types[2];
  void *arg_values[2];
  ffi_status status;
  struct test result;
  struct test arg;
  int input;

  // create the "test_struct_type" `ffi_type`
  test_struct_type.size = 0;
  test_struct_type.alignment = 0;
  test_struct_type.type = FFI_TYPE_STRUCT;
  ffi_type *test_elements[] = {
    &ffi_type_sint32,
    &ffi_type_sint32,
    &ffi_type_sint32,
    &ffi_type_sint32,
    &ffi_type_sint32,
    &ffi_type_uint8,
    &ffi_type_uint8,
    &ffi_type_uint8,
    &ffi_type_uint8,
    &ffi_type_uint8,
    &ffi_type_uint8,
    NULL
  };
  test_struct_type.elements = test_elements;
  printf("number of test.elements: %d\n", (int)(sizeof(test_elements) / sizeof(ffi_type *)));

  // populate argument fields
  arg.array[0] = 1;
  arg.array[1] = 2;
  arg.array[2] = 4;
  arg.array[3] = 8;
  arg.array[4] = 16;
  arg.str[0] = 'H';
  arg.str[1] = 'e';
  arg.str[2] = 'l';
  arg.str[3] = 'l';
  arg.str[4] = 'o';
  arg.str[5] = '\0';

  input = 69;

  // specify the "ffi_type *" to use for each argument
  arg_types[0] = &test_struct_type;
  arg_types[1] = &ffi_type_sint32;

  // Prepare the ffi_cif structure.
  printf("before prep_cif()\n");
  status = ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 2, &test_struct_type, arg_types);
  printf("after prep_cif()\n");
  if (status != FFI_OK) {
    // Handle the ffi_status error.
  }

  arg_values[0] = &arg;
  arg_values[1] = &input;

  // Invoke the function.
  ffi_call(&cif, FFI_FN(fn), &result, arg_values);

  int i;
  for (i = 0; i < 5; i++) {
    printf("result.array[%d]: %d\n", i, result.array[i]);
  }
  printf("result.str as string: %s\n", &result.str[0]);

  return 0;
}