Re: UFFI-izing varargs



Frank Goenninger DG1SBG wrote:

While trying to write a (working) interface to the syslog family of C functions I came across the varargs problem:

The C function is defined as:

void syslog( int priority, const char *messae, ...)

Hm - how to transform this into a suitable UFFI definition
and how to call it then ?

I have so far:

###

;; FUNCTION DEFINITION

(uffi:def-function ("syslog"   _syslog)
		   ((priority  :int)
		    (message   :cstring))
		   :returning  :void)

;; SYSLOG: CALLING THE C FUNCTION

(defun syslog (priority message &rest args)

  (declare (ignorable args))

  ;; write message to syslog

  (with-cstring (c-message message)
    (_syslog priority c-message))
)

###

That's obviously only half of the thing I want. So,
my questions are:

1. How to deal with the &rest args ?

Don't you want an array of pointers where you have (message :cstring) in the UFFI definition? Then you just populate the Lisp array (suitably defined using UFFI) and pass that.

   Is this the right approach ?

2. How to call `format' to transform the args into one
   string which can then be passed to syslog ?

I see that using approach 2) properly there's no need
for a varargs definition any more. So, 2) means how to
loop ober the args ... Oh, wait, that should be easy ;-)
It once again shows that I am still a newbie.

For fun you can look at format args ~{/~} to explore handily formatting a list.

kenzo

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