Use another language to call a function: Difference between revisions
Use another language to call a function (view source)
Revision as of 23:23, 19 June 2017
, 6 years ago→Using cptr and memcpy: Nuke trailing spaces.
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An alternative approach is possible if we avail ourselves of the <code>memcpy</code> function via FFI. We can receive the data as an opaque foreign pointer represented by the <code>cptr</code> type. We can set up <code>memcpy</code> so that its destination argument and return value is a <code>cptr</code>, but the source argument is a string:
<lang txrlisp>(with-dyn-lib "./query.so"
(deffi query "query" void (closure)))
(with-dyn-lib nil
(deffi memcpy "memcpy" cptr (cptr str size-t)))
(deffi-cb query-cb int (cptr (ptr (array 1 size-t))))
(query (query-cb (lambda (buf sizeptr) ; int lambda(void *buf,
(symacrolet ((size [sizeptr 0])) ; { #define size sizeptr[0]
(let* ((s "Here am I") ; char *s = "Here am I";
(l (length s))) ; size_t l = strlen(s);
(cond ; if (length > size)
((> l size) 0) ; { return 0; } else
(t (memcpy buf s l) ; { memcpy(buf, s, l);
(set size l)))))))) ; return size = l; } }</lang>
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