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List:       racket-users
Subject:    [racket] FFI: Casting pointers
From:       mflatt () cs ! utah ! edu (Matthew Flatt)
Date:       2012-01-23 14:12:34
Message-ID: 20120123141236.05F366500A8 () mail-svr1 ! cs ! utah ! edu
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Although discussion has moved on to better solutions...

At Sun, 22 Jan 2012 14:14:47 -0700, Michael W wrote:
> If I say:
> 
>    (cast
>     (malloc _OggVorbis_File)
>     _pointer _OggVorbis_File-pointer)
> 
> ...That's bad -- because I never keep the original pointer
> returned by the (malloc) call, the garbage collector reclaims
> that memory even though the _OggVorbis_File-pointer still points
> to it.

To fix this cast, use `_gcpointer' as the source type and `_gcable' on
the result pointer type:

    (cast
     (malloc _OggVorbis_File)
     _gcpointer
     (_gcable _OggVorbis_File-pointer))


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