Re: s48_extract_string?

   Date: Sat, 28 Feb 2009 13:46:47 +0100
   From: Donald Allen <[email protected]>

   I get

   > (load-dynamic-externals "/home/dca/Scheme48/test.so" #f #f #f)

   Error: vm-exception
          os-error
          (call-external-value "shared_object_dlopen"
   "/home/dca/Scheme48/test.so: undefined symbol: s48_extract_string")

   If I substitute a call in the C code to, say, s48_extract_byte_vector,
   then load-dynamic-externals is happy.

The documentation appears to be outdated.  Since Scheme48 1.5 or so,
when R6RSoid support for Unicode was introduced, s48_extract_string
has been no more.  Instead you must use `OS strings' on the Scheme
side and translate them to byte vectors for C use.  The relevant `OS
string' procedures are provided by the OS-STRINGS structure For
instance, here is how Scheme48's POSIX library currently wraps
getenv(3):

;;; scheme/proc/posix-env.scm

(define (lookup-environment-variable name)
  (cond
   ((external-lookup-environment-variable
     (os-string->byte-vector
      (x->os-string name)))
    => x->os-string)
   (else #f)))

(import-lambda-definition external-lookup-environment-variable (name)
  "posix_get_env")

;;; c/posix/proc-env.c

static s48_value
posix_get_env(s48_value name)
{
  char *value;

  value = getenv(s48_extract_byte_vector(name));

  return (value == NULL) ? S48_FALSE : s48_enter_byte_string(value);
}