Re: cffi: calls with variable number of arguments determined at runtime

Lars Rune Nøstdal <larsnostdal@xxxxxxxxx> writes:

cffi> (with-foreign-pointer-as-string (s 100)
(foreign-funcall "sprintf"
:pointer s
:string "i: %d"
:int 1234
:int))
"i: 1234"


;; ..works ok.. same with..


cffi> (defcfun "sprintf" :int
(str :pointer)
(control :string)
&rest)
sprintf
cffi> (with-foreign-pointer-as-string (s 100)
(sprintf s "i: %d" :int 1234))
"i: 1234"


;; but what if i do not know the types and arguments at compile time?
;; these are stupid examples and none of them work, but:


cffi> (with-foreign-pointer-as-string (s 100)
(let ((type-args* '(:int 1234)))
(sprintf s "i: %d" type-args*)))

Obviously, here you know the type, since you wrote %d, not %s or %f!

Now imagine you have this C function:

void format(const char* ctrlstring,int nargs,void** arguments){
...
}

How can you write it in C, if you don't know the type of the
arguments? The same as you'd do in lisp, and the same printf does,
you parse ctrlstring to collect the types.



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