4.2.3 Passing a constant string

Use of the :reference-pass type in this example converts the Lisp string to a foreign string on calling, but does not convert the string back again on return.

Here is the C code for the example. It uses the argument string but returns an integer.

Windows version:

#include <string.h>

#include <ctype.h>

__declspec(dllexport) int __cdecl count_upper(const char *string)

{

  int count;

  int len;

  int ii;

  count = 0;

  len = strlen(string);

  for (ii = 0; ii < len ; ii++)

      if (isupper(string[ii]))

         count++;

  return count;

}

Linux/Unix/Macintosh version:

#include <string.h>

#include <ctype.h>

int count_upper(const char *string)

{

  int count;

  int len;

  int ii;

  count = 0;

  len = strlen(string);

  for (ii = 0; ii < len ; ii++)

      if (isupper(string[ii]))

         count++;

  return count;

}

Here is the foreign function definition using :reference-pass :

(fli:define-foreign-function (count-upper "count_upper" :source)

                             ((string (:reference-pass :ef-mb-string)))

                             :result-type :int

                             :language :c

                             :calling-convention :cdecl)

(count-upper "ABCdef")

=>

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LispWorks Foreign Language Interface User Guide and Reference Manual - 7 Dec 2011