[Openmcl-devel] How do I initialize an array of structs? (FFI)

David Steuber david at david-steuber.com
Sat Jan 8 23:46:32 UTC 2005


On Jan 8, 2005, at 3:17 AM, David Steuber wrote:

> Give this C fragment:
>
> EventTypeSpec moonSpec[] = {{kEventClassCommand, kEventCommandProcess},
>   {kEventClassWindow, kEventWindowClose}};
>
> How do I initialize moonspec in the following rlet?
>
>   (rlet ((nibref :<ibn>ib<r>ef)
>          (mainspec :<e>vent<t>ype<s>pec
>                    :event<c>lass #$kEventClassCommand
>                    :event<k>ind #$kEventCommandProcess)
>          (moonspec (:array :<e>vent<t>ype<s>pec 2)))
>     ...)
>
> I tried doing it in the rlet until I found this:
>
> " When the type is an array,  initforms  may  not be provided, because 
>  make-record   cannot initialize its values.  make-record   is also 
> unable to initialize fields of a  struct   which are themselves   
> struct   s. The user of   make-record   should set these values  by 
> another means."

Ok, after much hunting through the docs and a couple of aborted 
attempts, I came up with this:

   (rlet ((nibref :<ibn>ib<r>ef)
          (mainspec :<e>vent<t>ype<s>pec
                    :event<c>lass #$kEventClassCommand
                    :event<k>ind #$kEventCommandProcess)
          (moonspec (:array :<e>vent<t>ype<s>pec 2)))
     (let ((offset 0))                                 ; initialize 
moonspec the only way I know how
       (dolist (sfv (list #$kEventClassCommand #$kEventCommandProcess 
#$kEventClassWindow #$kEventWindowClose))
         (setf (ccl::%get-unsigned-long moonspec offset) sfv)
         (incf offset (ccl::record-length :unsigned))))

I had a bit of confusion over two points.  #$Foo becomes OS::|Foo| so 
using a quoted list didn't work like I thought it would, hence LIST.  I 
also thought %GET-UNSIGNED-WORD would be 32 bits, not 16.  Oops.  Both 
facts are documented though, the latter in 9.3.2.1 in the OpenMCL 
documentation.

Is this the best way to do this?




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