Re: Calls to alien functions taking struct pointer parameters...

[andrew]

Thanks Raymond.

I agree (alien:* t) seems like the right choice.  I'll try this 
again--I did try this previously but now I'm thinking I wasn't handling 
the return type correctly, this too needs to be (alien:* t) for this 
all to work.

For example, if I'm using something like this:

NAME
          glXGetCurrentDisplay - get display for current context


     C SPECIFICATION
          Display * glXGetCurrentDisplay( void )


The correct def-alien-routine woud look like:

(alien:def-alien-routine (glxgetcurrentdisplay "glXGetCurrentDisplay") 
(alien:* t))

which should then work nicely with:


  (alien:def-alien-routine ( glxqueryextension "glXQueryExtension" )
    c-call:unsigned-int
    ( dpy (alient:* t) :in )
    ( errorBase (alient:* t) :in )
    ( errorBase (alient:* t) :in )

--Andrew

-----Original Message-----
From: Raymond Toy <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]
Sent: Tue, 23 Nov 2004 09:37:01 -0500
Subject: Re: Calls to alien functions taking struct pointer 
parameters...


>>>>> "Andrew" == Andrew Simms <[EMAIL PROTECTED]> writes:

     Andrew> I've been working on some code to port a Lisp based 
software system
from
     Andrew> AllegroCL to CMUCL.  Part of this project involves making 
calls to
OpenGL
    Andrew> calls via functions like this one:

    Andrew>    NAME
    Andrew>       glXQueryExtension - indicate whether the GLX extension is
    Andrew>       supported


    Andrew>      C SPECIFICATION
    Andrew>       Bool glXQueryExtension( Display *dpy,
    Andrew>                               int *errorBase,
    Andrew>                               int *eventBase )

     Andrew> The Lisp code does not ever try to build things like the 
*dpy
parameter from
     Andrew> scratch.  Instead it gets these from calling other GL 
functions
which return
     Andrew> a pointer to a properly constructed struct of type Display. 


    Andrew> The problem I see is that I'm not sure how to do this with
    Andrew> def-alien-routine:

     Andrew> (alien:def-alien-routine ( glxqueryextension 
"glXQueryExtension" )
    Andrew> c-call:unsigned-int
     Andrew>    ( dpy c-call:integer :out )  ;; try to wedge in a generic 
integer
    Andrew> pointer, doesn't work
    Andrew>     ( errorBase c-call:integer :out )
    Andrew>       ( errorBase c-call:integer :out )

     Andrew> And using something like '(alien:* T) is not compatible 
with :out
style
    Andrew> arguments.

I think an (alien:* t) is the right type.  But for glXQueryExtension,
don't you want just plain :in style argument?  You are passing an
alien pointer into the function.  The function is free to modify the
memory contents pointed to by the pointer.

I'm guessing though.

Ray