Defining callback functions with varargs

Hi everyone,

currently I’m trying to define a callback function in Lispworks that accepts varargs (as that is the defined interface for the callback), i.e. the defined callback must match the following signature:

void myCallback(Component c, myString name, myStatus status, myString category,

myString message, ....);

Defining a similar callback from Lisp for the non-variable arguments is simple, e.g.

(fli:define-foreign-callable ("myCallback" :result-type :void :calling-convention :cdecl)

((component component-ptr)

(name (:reference-return my-string))

(status my-status)

(category (:reference-return my-string))

(message (:reference-return my-string)))

…)

However for the access to the remaining arguments I’d need access to the stack-pointer to access and manually convert the arguments based on the message string, and I can’t find anything related to that in the documentation…

Has anyone done something like this?

Regs, Pierre.

Pierre R. Mai <pmai@pmsf.de>

PMSF IT Consulting Pierre R. Mai http://www.pmsf.de/

Blumenstr. 4 Goethestr. 32

85417 Marzling 87724 Ottobeuren

Tel. +49(0)8161/935 35 12 +49(0)8332/936 69 13

Fax +49(0)8161/935 35 08 +49(0)8332/936 69 03

VAT ID / USt-ID Nr: DE 212838159 Germany

Re: Defining callback functions with varargs

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Re: Defining callback functions with varargs

If you have access such that you can change the function signature, could you just pass a va_list instead and then pass that to vsprintf from within the Lisp code (I assume you are logging or similar, and "message" is the format)?

void myCallback(..., string msg, va_list args);

Now, for your foreign callable, args is just an integer/pointer you can pass to vsprintf() from within your lisp code.

Jeff M.

Pierre R. Mai

Monday, August 05, 2013 10:34 AM

Hi everyone,

currently I’m trying to define a callback function in Lispworks that accepts varargs (as that is the defined interface for the callback), i.e. the defined callback must match the following signature:

void myCallback(Component c, myString name, myStatus status, myString category,
myString message, ...);

Defining a similar callback from Lisp for the non-variable arguments is simple, e.g.

(fli:define-foreign-callable ("myCallback" :result-type :void :calling-convention :cdecl)
    ((component component-ptr)
     (name (:reference-return my-string))
     (status my-status)
     (category (:reference-return my-string))
     (message (:reference-return my-string)))
…)

However for the access to the remaining arguments I’d need access to the stack-pointer to access and manually convert the arguments based on the message string, and I can’t find anything related to that in the documentation…

Has anyone done something like this?

Regs, Pierre.

--
Pierre R. Mai                                        <pmai@pmsf.de>
PMSF IT Consulting Pierre R. Mai                http://www.pmsf.de/
Blumenstr. 4                                          Goethestr. 32
85417 Marzling                                     87724 Ottobeuren
Tel. +49(0)8161/935 35 12                      +49(0)8332/936 69 13
Fax +49(0)8161/935 35 08                      +49(0)8332/936 69 03
VAT ID / USt-ID Nr: DE 212838159                            Germany