From: Daniel Berger <djberg96@...>
Date: 2009-08-08T01:45:49+09:00
Subject: Re: FFI, sysctl, pointer question

Andrea Fazzi wrote:
> Daniel Berger wrote:
>> Hi,
>>
>> I'm trying to get better at FFI, but I'm getting stumped on how to
>> create and pass pointers to functions.
>>
>> In the example below, in the Sys::Uptime.seconds method, I'm trying to
>> figure out how to create and pass a pointer for the mib (a 2-element
>> integer array) and the timeval size (i.e. where I have a '?' instead of
>> actual code).
>>
>> What should the actual code be?
> 
> You could explicity instantiate two MemoryPointer objects initialized 
> with
> the proper values:
> 
>   mib_ptr = FFI::MemoryPointer.new(:int, 2).write_array_of_int(mib)
>   tv_size_ptr = FFI::MemoryPointer.new(:int).write_int(tv.size)
> 
> Then you could pass those values to sysctl function:
> 
>   sysctl(mib_ptr, 2, tv, tv_size_ptr, nil, 0)

Thank you, that worked.

> To ask for more (and better) help feel free to post your questions to 
> the Ruby-FFI ml at users@ruby-ffi.kenai.com

If we want FFI to gain traction among Rubyists (we do, don't we?), it's 
better to ask & answer here IMO.

Regards,

Dan