Re: [Chicken-users] pointer-pointer-ref

[Nicholas \"Indy\" Ray]

Something simular to you're pointer-pointer-ref is what I was using.
and semantically it seems to be best.

Indy

On Thu, Mar 12, 2009 at 6:25 PM, Eduardo Cavazos <address@hidden> wrote:
> Eduardo Cavazos wrote:
>
>> XQueryTree is a function from xlib:
>>
>> extern Status XQueryTree(
>>    Display*        /* display */,
>>    Window        /* w */,
>>    Window*        /* root_return */,
>>    Window*        /* parent_return */,
>>    Window**        /* children_return */,
>>    unsigned int*    /* nchildren_return */
>> );
>>
>> This is how I'm pulling it into Chicken (using a 'c-function' macro I'm
>> using for cross-Scheme compatability):
>>
>> (c-function Status XQueryTree
>>  (Display*
>>   Window
>>   u32vector
>>   u32vector
>>   (c-pointer (c-pointer unsigned-long))
>>   u32vector))
>>
>> The tricky parameter is the 'Window**' one.
>>
>> I can allocate enough storage for a pointer via:
>>
>>    (define children-return (allocate sizeof:c-pointer))
>>
>> The trouble is, how do I portably extract the address? If I assume a
>> 32-bit pointer size, it's easy:
>>
>>  (pointer-u32-ref children-return)
>>
>> on a 64-bit machine, that should be:
>>
>>  (pointer-u64-ref children-return)
>>
>> but, there is no 'pointer-u64-ref'. :-)
>>
>> Once I have the address, the rest is easy; convert it to a pointer with
>> address->pointer, and extract individual windows with pointer-u32-ref.
>>
>> For reference, Ypsilon has this procedure that I use in this sort of case:
>>
>>    bytevector-c-void*-ref
>>
>> Larceny has:
>>
>>    %get-pointer
>
> Instead of pointer-u32-ref, or pointer-u64-ref, looks like I can have a
> pointer-pointer-ref, which is similar to the Ypsilon and Larceny procedures
> I mentioned:
>
> (define pointer-pointer-ref
>  (foreign-lambda*
>   c-pointer
>   ((c-pointer ptr))
>      " C_return ( * ( ( void** ) ptr ) ) ; "))
>
> I can proceed with that, but I'm still open to any suggestions! :-)
>
> Ed
>
>
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