CFFI calling char* with a vector

call.lisp

(ql:quickload :cffi)
(cffi:define-foreign-library vowels (t (:default "/path/to/libvowels")))
(cffi:use-foreign-library vowels)

(defvar *vector* #(104 101 108 108 111))
(print (cffi:foreign-funcall "vowels" :string (map 'string #'code-char *vector*) :int))
# prints out 2

compile.sh

gcc vowels.c -shared -o libvowels.so

vowels.c

#include <string.h>

int vowels(char *str) {
    int count = 0;
    for (int i = 0; i < strlen(str); ++i) {
        switch (str[i]) {
        case 'a':
        case 'e':
        case 'i':
        case 'o':
        case 'u':
            count++;
            break;
        default:
            break;
        }
    }
    return count;
}