The example from the libffi docs for how to use `ffi_closure` with `ffi_closure_alloc()` and `ffi_closure_free()`.

ffi_closure_alloc_test.c

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

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

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

  int (*bound_puts)(char *);
  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_uint, args) == FFI_OK)
    {
      /* Initialize the closure, setting stream to stdout */
      if (ffi_prep_closure_loc(closure, &cif, puts_binding,
            stdout, bound_puts) == FFI_OK)
      {
        printf("Before bound_put()\n");
        rc = 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;
}

How this can be used to call a function without compile-time knowledge of its name and arguments?