Use another language to call a function: Difference between revisions
Use another language to call a function (view source)
Revision as of 20:12, 8 June 2017
, 6 years ago→Using cptr and memcpy: Show C side-by-side.
(→{{header|TXR}}: Break into sections; add cptr-memcpy based solution.) |
(→Using cptr and memcpy: Show C side-by-side.) |
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Line 1,177:
(deffi-cb query-cb int (cptr (ptr (array 1 size-t))))
(query (query-cb (lambda (buf sizeptr) ; int lambda(void *buf, size_t
(symacrolet ((size [sizeptr 0])) ; { #define size
(let* ((s "Here am I") ; char *s = "Here am
(l (length s))) ; size_t l =
(cond ; if (length >
((> l size) 0) ; { return 0; }
(t (memcpy buf s l) ; { memcpy(buf, s,
(set size l)))))))) ; return size = l; } }</lang>
Here, the use of the <code>str</code> type in the <code>memcpy</code> interface means that FFI automatically produces a UTF-8 encoding of the string in a temporary buffer. The pointer to that temporary buffer is what is passed into <code>memcpy</code>. The temporary buffer is released after <code>memcpy</code> returns.
To reveal the similarity between the Lisp logic and how a C function might be written, the corresponding C code is shown.
However, that C code's semantics is, of course, devoid of any hidden UTF-8 conversion.
=={{header|zkl}}==
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